CHEMICAL ANALYSIS.
(1) The total solids are ascertained by evaporating a given quantity of the water to dryness, and weighing.
(2) Determination of Chlorine (see page [81]).
(3) Determination of Hardness (see page [80]).
(4) The Determination of Nitrites is based on the reddish-brown colouration produced when an acid solution of metaphenylene diamine is brought into contact with a weak solution of nitrous acid. 100 c.c. of the water under examination are placed in a clean glass cylinder. Add 1 c.c. of H₂SO₄ solution (1 in 3), then 2 c.c. of metaphenylene diamine solution (5 grains in 1 litre of water with a little H₂SO₄ added). Stir well with a glass rod. If a colouration is produced at once, a smaller quantity of water must be taken, and made up to 100 c.c. with pure distilled water. The quantity of nitrous acid present is measured by introducing different fractions of a c.c. of the standard sodium nitrate solution[3] into similar glass cylinders. Each is then made up to 100 c.c. with distilled water, and the metaphenylene diamine solution and acid added as before. The colour develops slowly; time must, therefore, be allowed in matching.
(5) The Determination of Nitrates can be conveniently made by the following method. When phenyl-hydrogen sulphate solution is poured upon a nitrate, and sulphuric acid is formed, picric acid is formed:—
(C₆H₅)HSO₄ + 3 HNO₃ = C₆H₂(NO₂)₃OH + H₂SO₄ + 2 H₂O.
The addition of free ammonia in excess forms yellow ammonium picrate, the intensity of the colour of which is an index of the picrate, and of the nitrate from which it was produced. (a) Evaporate 25 c.c. of the water under examination, and (b) 5 c.c. of standard KNO₃ solution (containing 1 part N in 100,000) to dryness in two porcelain dishes over the water bath. Add 1 c.c. of phenyl-sulphate solution to each of these as soon as cool, stir well with a glass rod, then add 1 c.c. distilled water to each dish and 3 drops of strong H₂SO₄. Next add 25 c.c. of water to each dish, and after heating for five minutes over the water bath, add solution of ammonia to each dish in excess. A yellow colour is produced in proportion to the amount of nitrate present. Transfer the liquids to glass cylinders, and dilute each to 100 c.c. Take 50 c.c. of the solution showing the least colour, and dilute the other with distilled water, until it has the same tint.
Supposing the 100 c.c. of the sample required to be diluted to 150 c.c.—
Then the amount of N will be 150 ∕ 100 × 5 ∕ 25 = ·3 parts per 100,000.
If the two solutions (a) and (b) when diluted have the same tint, then the
Amount of N in the sample = 5 ∕ 25 = ·2 parts per 100,000.
(6) Determination of Organic Matter. Frankland’s combustion process involves the use of delicate and costly apparatus, and is seldom employed. In this process the organic carbon is evolved as carbonic acid, and the nitrogen as such.
Wanklyn’s ammonia process is based on the reduction of organic matter to ammonia. Part of this ammonia, free or saline ammonia, is simply combined with carbonic, nitric, or other acids, or is easily derived from the urea of urine, CH₄N₂O + 2H₂O = 2(NH₄)₂CO₃. Another part is only set free when the water is boiled with a strongly alkaline solution of permanganate of potassium. This is called the albuminoid ammonia.
In carrying out this method, a retort is taken, and after having been washed out, first with a little sulphuric acid, and then with some of the water to be analysed, 500 c.c. of the latter is put in, and the retort is connected with a condenser, and distillation begun; 50 c.c. of the distilled water is collected in a cylindrical glass tube called a Nessler glass. To this 1½ c.c. of Nessler’s reagent (mercuric iodide dissolved in a solution of potassic iodide and made alkaline by potass) are added. A rich brown colour is produced, if any ammonia is present in the distillate. The amount of ammonia in the distillate is determined by exactly imitating its colour by adding a known quantity of a standard solution of ammonium-chloride to 50 c.c. of ammonia-free distilled water, and then Nesslerising as before. Each c.c. of the dilute standard ammonium chloride solution is equivalent to ·00001 gramme of ammonia (NH₃).
If the first 50 c.c. of water distilled over gives only a slight colouration with the Nessler solution, no more water needs to be distilled over for free ammonia. If more is present, two more 50 c.c.’s must be distilled over, and the amounts of the standard solution required for imitating the test in each Nesslerised 50 c.c. added together. Thus, if 2 c.c. were needed. This
= ·00002 grm. NH₃, which is contained in 500 c.c. of the water
= ·00002 × 200 = ·004 parts saline NH₃ in 100,000 of water.
The free ammonia having been distilled over, 50 c.c. of an alkaline permanganate solution (containing 8 grammes KMnO₄ and 200 grammes of NaOH in 1100 c.c. of distilled water, boiled until the bulk is reduced to 1,000 c.c.) is poured into the retort, and distillation is begun again. Three successive 50 c.c.’s of water are collected, and then the distillation stopped. Each of these is Nesslerised, and the tint imitated as before with standard ammonia solution. The three amounts of ammonia thus found to be present are added together; and when multiplied by 200, we obtain the amount of albuminoid ammonia in 100,000 parts of water. This test is universally employed by water analysts along with the next test.
The amount of Oxygen Absorbed from permanganate of potassium is regarded as an approximate test of the amount of organic matter in water. Qualitatively this forms a favourite method of testing the purity of water. Two glass cylinders are taken, one filled with distilled water, one with the water to be tested. To each is added a given small amount of an acid solution of permanganate of potassium. The distilled water to which permanganate has been added will retain its pink colour; while, if the water being tested is very impure, it will speedily become decolourised. The rapidity and degree of decolourisation are a rough test of the amount of impurity. A rapid decolourisation proves the presence of organic matter having an animal origin, or of sulphuretted hydrogen, iron, or nitrites. Sulphuretted hydrogen is rarely present, and can be easily recognised by its smell; iron or nitrites are readily distinguished by their appropriate tests. In the absence of these, the rapid discolouration is an indication of animal contamination.
To Determine the Amount of Oxygen Absorbed, two glass-stoppered bottles, each holding about 350 c.c. are required. Into one, 250 c.c. distilled water, and into the other the same amount of the water under examination are placed. To each are then added 10 c.c. of standard permanganate of potassium solution[4] and 10 c.c. of a standard pure 25 per cent sulphuric acid solution. The two bottles, after being shaken, are placed in a water-bath at 27°C for four hours. At the end of this time add a few drops of potassium iodide solution to each bottle. The pink is now replaced by a yellow colour.[5] A standard thiosulphate solution (Na₂S₂O₃, 5H₂O)[6] is placed in a burette. From this the thiosulphate solution is run into the control bottle until the yellow colour almost disappears. Now a few drops of starch solution are added, and a blue colour is produced. The thiosulphate is then added cautiously until all the blue colour disappears. The amount of thiosulphate necessary for this is read off on the burette. The same process is repeated with the bottle containing the sample of water. The starch acts as an indicator. The amount of iodine liberated is an index of the amount of permanganate in the water, which has not been used up by its impurities. The amount of iodine liberated is measured by the amount of thiosulphate required to decolourise the solution. Thus—
2 Na₂S₂O₃ + I₂ = 2 NaI + Na₂S₄O₆.
Suppose that 20 c.c. of thiosulphate solution were required to decolourise the iodine liberated in 250 c.c. of a sample of water, while the distilled water required 25 c.c. Then 25 c.c. thiosulphate represents 10 c.c. of the permanganate solution = ·001 grains of available oxygen.
25-20 = 5
As 25 c.c. = ·001 grm. O, 5 c.c. = 5 ∕ 25 of ·001 = ·0002 grm.
This is the amount of O absorbed by 250 c.c. of the sample.
Therefore the amount of O absorbed by 100,000 c.c. of the sample. = ·08 grm.
It is usual to make a similar determination of the amount of oxygen absorbed in fifteen minutes.
The Interpretation of Results of analysis is more difficult than the analysis. A single analysis may be misleading, unless the source of the water is known. Constancy in composition or analysis is almost as important a criterion of purity as the actual character of the constituents. A knowledge of the source is essential in interpreting results of analysis, as the chemical composition of water varies with its source. The following rules are only approximately correct, and are subject to the above general considerations. The total dissolved solids in river-water are usually 10 to 30 parts in 100,000. Shallow well-water may contain from 30 to 200 parts or even more, and deep well-water from 20 to 70 parts.
Saline Ammonia in water is commonly of animal origin, ammonia (NH₃) being one of the first products of decomposition of nitrogenous animal refuse. Upland surface water usually contains about ·002 parts per 100,000, but it may reach ·008 or more if the land over which the water passes has been manured. Shallow well-water may be free from ammonia, or this may be very excessive in amount. Deep well-water may contain no ammonia or any amount up to ·1 per 100,000. Its presence is suspicious if the albuminoid ammonia is above a trace, or if the oxygen absorbed is appreciable in amount. Generally water is suspicious if saline ammonia is up to ·01 per 100,000. Albuminoid Ammonia indicates the amount of organic nitrogenous matter present in the water. It should not exceed ·005 parts per 100,000, while at the same time the saline ammonia should not usually exceed ·01 per 100,000. For Oxygen consumed the following table of the weight of oxygen required for 100,000 parts of water is given by Clowes and Coleman:—
| UPLAND SURFACE WATER. | WATER FROM OTHER SOURCES. | |
|---|---|---|
| Water of Great purity | Not exceeding ·1 | Not exceeding ·05 |
| Medium purity | From ·1 to ·3 | From ·05 to ·15 |
| Doubtful purity | From ·3 to ·4 | From ·15 to ·20 |
| Impure | Exceeding ·4 | Exceeding ·20 |
The presence of more than 1 and still more so of 2 grains of Chlorine per 100,000 of water is most suspicious, except in saline districts. Nitrites if present in an appreciable quantity indicate comparatively recent contamination by sewage. In deep well-water they may be produced by deoxidation of nitrates. Nitrates in upland surface waters should not be equivalent to more than ·03 of N. per 100,000; in shallow well-waters the amount varies greatly; in deep well-waters it may be excessive. As a rule it ought not to be equivalent to more than 5 parts of N. per 100,000 of water; but the significance of nitrates depends greatly on the source of the water and on the amount of the other constituents present.
Chemical analysis alone cannot ascertain the safety of a given drinking water. A minute amount of impurity inappreciable to analysis may be competent to produce disease; while another water may be drunk with impunity, which contains considerable organic matter. Chemical analysis “can tell us of impurity and hazard, but not of purity or safety” (Buchanan). An accurate opinion as to the character of a drinking water can only be expressed when one knows the amount of each chief constituent (as above), and whether these amounts deviate from the same water at other times or from other waters in the vicinity.
[CHAPTER XII.]
ORIGIN AND EFFECTS OF THE IMPURITIES OF WATER.
Origin of Impurities of Water.—Parkes classifies impurities of water as:
1. Those Received at the Source.—The character of water varies with the geological structures through which it has passed; with its origin from the subsoil or cultivated land, or deep wells, or graveyards, or near the sea, etc. It is a mistaken policy to commence with an impure water and proceed to purify it; though communities supplied from rivers may be compelled to submit to this. They must then insist on the most stringent measures of purification (see p. 96). Inorganic impurities are of much smaller consequence as regards health than organic; hence the great advantage of deep well-water over river water. It has been suggested, however, that when deep well-water becomes polluted, it is more dangerous than equally polluted river-water, because in the latter the normal bacteria of water are more abundant, and possibly interfere with the continued life in water of disease-producing bacteria. This statement is unproved; and if correct, is rather an indication for further precautions being taken to prevent access of pollution to deep wells, than in favour of the continued use of river-water.
2. Impurities of Transit from Source to Reservoir, acquired during the flow in rivers, canals, or other conduits. These impurities have been broadly divided by the Rivers Pollution Commissioners into “sewage” and “manufacturing;” the former including the solid and liquid excreta, the house and waste water, etc.; the latter including the refuse from manufacturing processes, as from dye and bleaching works, tanneries, etc.
3. Impurities of Storage, whether in wells, reservoirs, or cisterns. Organic impurities are commonly received at this stage. A well, for instance, drains the soil around it in the shape of an inverted cone, with a very broad base, unless the entrance of water from its sides is prevented.
4. Impurities of Distribution. Lead, and occasionally other metals, are dissolved by certain waters. If the pipes are left empty, as with an intermittent supply, sewage may be drawn into them; in a few cases coal-gas has found its way into the water pipes (page [76]).
Effects of Impure Water.—1. Effects of Mineral Impurities. Suspended Mineral matters in unfiltered water occasionally produce diarrhœa. The hill diarrhœa of some parts of India has been traced to water containing fine mica particles in suspension.
Hard water is said by some to be hurtful, but the salts causing hardness are probably innocuous when not amounting to more than 12 or 16 grains per gallon. Persons in the habit of drinking hard water find soft water unpalatable. Hard water has been thought to favour gout and calculus (stone), but this is not so. The salts producing permanent hardness are said to be injurious, producing indigestion, but this is doubtful in the amounts ordinarily drunk.
Goitre, a swelling of the thyroid gland in the neck, is often associated with the use of drinking water from magnesian limestone formations; but that any kind of excessively hard water causes goitre is very doubtful.
Lead dissolved in water may produce serious and lasting ailments, and they are often present for a long time before their cause is detected. The amount of lead capable of producing poisonous symptoms has been as little as 1 ∕ 100 grain per gallon of water (Dr. Angus Smith). According to De Chaumont, 1 ∕ 10 grain per gallon, that is 1 part in 700,000 is usually required to produce such symptoms. In the well-known case of the poisoning of Louis Phillippe’s family at Claremount, there was 7 ∕ 10 grain of lead in a gallon of water; and this affected 34 per cent. of those who drank it. The symptoms produced by lead poisoning are those of indigestion, accompanied by colic; a blue line at the junction of the gums with the teeth; “wrist drop,” a paralysis of the muscles of the forearm, or some other paralysis; and if the poisoning is continued, attacks of gout, followed by its usual consequences, chronic kidney disease. The latter affections chiefly occur when the poisoning is continued for a long time, as in the case of painters or type-setters: poisoning from water is generally discovered before any other than dyspeptic symptoms and colic are produced.
The presence of traces of iron in water may give it a slightly astringent taste; and such water is liable to cause headache and constipation.
2. Effects of Vegetable Impurities.—Living plants are unobjectionable, but decomposing vegetable matter may produce diarrhœa and other severe symptoms.
3. Effects of Animal Impurities.—Animal impurities of water are by far the most important from a sanitary point of view. They are most commonly derived from leaky drains or cesspools, or from surface accumulations of filth. The quality of the contamination is more important than its quantity; and this will explain why water containing a large amount of sewage may be drunk for a prolonged period with impunity, while at another time the least trace, if it contain the active germs of disease, will lead to serious mischief.
Suspended animal impurities are much more dangerous than those completely dissolved. Hence the examination of the colour and turbidity of drinking water is very important. Fæcal contamination is by far the most dangerous of all, and chiefly so when it is derived from a patient suffering from some communicable disease, like enteric fever or cholera.
Certain Parasites occasionally are swallowed with water in the form of embryo or egg. The liver fluke, round worm, and less frequently other kinds of entozoa have been introduced in this way. The occasional swallowing of small leeches has occasionally given rise to hæmorrhage.
Diarrhœa may be caused by animal contamination of water. It most often occurs in summer, when all the circumstances are favourable to active fermentative changes. The summer diarrhœa of infants is caused by similar changes in milk or other foods. The presence of fœtid gases in water may lead to diarrhœa. This may occur when the overflow pipe of a cistern opens into the soil pipe or into the trap of the W.C.
Dysentery, like cholera and enteric fever, may be propagated by water contaminated with the stools of a patient suffering from the same disease.
Malaria or Ague has been stated to be caused by the water of malarious marshes. The evidence on this point requires revision, in view of the part which the mosquito is now known to play in the propagation of this disease (pages 282 and 307).
Enteric (otherwise called Typhoid) fever is most often due to the drinking of water contaminated with sewage.
The balance of evidence is in favour of the view that in order to produce enteric fever water must be contaminated with the stools or urine of a patient who has suffered from this disease. Numerous instances are on record in which villages, the inhabitants of which drink sewage-contaminated water, have remained free from enteric fever, until a patient suffering from it has come to the village, when the spread by water has been very rapid. Occasionally no known contamination from a case of enteric fever has preceded the outbreak of this disease which has been caused by sewage-contaminated water. It must be remembered on this point that the urine of an enteric fever patient may occasionally contain large numbers of the bacillus causing this disease for several months after the patient is well (page [301]).
The contamination of water with sewage may occur in various ways. In country places surface wells and small streams commonly supply the drinking water, and these are frequently contaminated. The illustration (Fig. 9) shows the percolation of excretory matters from an out-door closet through the porous gravel, into a neighbouring well; the result being an epidemic of enteric fever among those who drank the water of the well. Alterations in the level of the subsoil water are sometimes followed by an outbreak of enteric fever (p. 70). A sudden fall of rain occurs, and the excess of water in the soil absorbs the soakings from country privies or cesspools, and carries them into the nearest well. The percolation of tainted water through a considerable tract of land, possibly along fissures, is sometimes insufficient to purify it, as proved by a remarkable epidemic in the small village of Lausen, in Switzerland.
In other cases sewage gains access into leaky water-pipes. Formerly contamination was occasionally due to improper connection between the overflow pipe of the cistern and the soil-pipe, or to the water-closet being flushed by a pipe directly connected with a water-main (as in the Caius College outbreak at Cambridge), or connected with the drinking-water cistern (page [76]).
Milk may, by the admixture of water, become contaminated with enteric matter, and produce widespread epidemics. Where the water is very impure, the small amount used in washing cans may suffice to cause infection.
Cholera was first proved by Dr. Snow, in 1849, to be due to the specific contagium of cholera gaining an entrance into drinking water. This contagium is derived as in enteric fever from the intestinal evacuations, the urine, and the vomit of patients suffering from the same disease.
Fig. 9.
The close connection of the spread of cholera with an impure water supply has been repeatedly shown in this country. The cholera epidemic of 1854 was very severe in the southern districts of London. At that period these districts were supplied with water by the Southwark and Vauxhall Company, deriving its water from the Thames at Battersea, and by the Lambeth Company, having its intake at Thames Ditton, where the water was purer. The two companies were acting in rivalry, so that in many streets their mains ran side by side; and houses in the same street similar in all other respects, received a different water supply. An investigation of the distribution of cholera in these districts gave the following results:—
| POPULATION IN 1851. | CHOLERA DEATHS IN 14 WEEKS. | CHOLERA DEATHS PER 10,000 OF POPULATION. | |
| Houses supplied by Southwark Co. | 266,516 | 4,093 | 153 |
| Houses supplied by Lambeth Co. | 173,748 | 461 | 26 |
The facts, when examined in detail, brought out still more strikingly the exemption of the houses supplied by the Lambeth Company; the infection picking out in a given street the houses supplied by the Southwark Company. The great epidemic of cholera at Hamburg in 1892 proves the same point. Hamburg, Wandsbeck and Altona are three towns adjoining each other, and really forming one large community; but while Hamburg suffered terribly, the two other towns had no cases of cholera, except the few that were brought into them. In all respects except water-supply the conditions were alike; but Wandsbeck obtained filtered water from a lake, Altona obtained filtered water from the Elbe below the town, while Hamburg was supplied, previous to the epidemic, by unfiltered water from the Elbe just above the town.
Diphtheria and scarlet fever have never been traced to polluted water.
Effects of an Insufficient Supply of Water.—The influence on personal health is most baneful. Water is used sparingly for purposes of cleanliness, with the necessary results that cutaneous diseases become more common, and the whole body suffers; the linen is imperfectly and infrequently washed; the house becomes dirty; drains are imperfectly flushed; the streets are not cleaned; and the whole atmosphere becomes loaded with impurities. According to Parkes, it is probable that the almost complete disappearance of typhus fever from civilized and cleanly nations, is not merely owing to better ventilation, but also to more frequent and thorough washing of clothes.
Insufficient cleansing of the surfaces of streets and of sewers, owing to a deficient supply of water, has a very important influence on the spread of enteric fever and epidemic diarrhœa. A heavy fall of rain often causes a rapid diminution in the prevalence of the latter disease.
[CHAPTER XIII.]
THE PURIFICATION OF WATER.
When a public water-supply is provided, it may reasonably be expected to be furnished pure and fit for use; but this, occasionally is not so. The reports, for instance, of the condition of the London Water Supply, occasionally show that it is turbid and contains a slight excess of organic matter. This is especially the case when, after heavy rainfall, storm-water is brought into the reservoirs, and owing to deficient storage, sufficient time is not allowed for deposit. Rain-water always and other waters frequently require to be purified before use.
Methods of Purification.—The only certain way of obtaining pure water is by Distillation; but this plan is scarcely applicable to water on a large scale. Furthermore distilled water is not so palatable as ordinary water. The distillation of water is more especially required on board ship, during long voyages. It should be followed by the use of some measure to secure efficient aeration.
2. Boiling water serves to remove the temporary hardness, and the chalk carries down with it a large proportion of any organic matter that may be present. Boiling deprives the water of its dissolved gases, and renders it flat; it is desirable, therefore, to aerate it by filtration or from a gazogene after boiling. All the microbes which are known to produce disease are destroyed by efficient boiling. Certain putrefactive microbes are more persistent of life, owing to the fact that they form spores, which are not killed at the temperature of boiling water. Tyndall showed that by boiling the liquid containing these spore-forming microbes on three successive days, thus giving time for the spores to develop into less resistant microbes, they could be effectually destroyed. Boiled water will not cause enteric fever or cholera, the two chief water-borne diseases.
3. The exposure of water in divided currents to the air by passing it through a sieve has been proposed as a means of purifying water, but it is inefficient when trusted to alone. Plants in reservoirs help to absorb organic matter; and fish, by destroying small crustaceans, have been found useful. Hard waters do not bear exposure to light, as a thick green growth of chara occurs, which may block pipes, and give a bitter taste to the water.
4. The Addition of Chemical Substances.—(1) Clarke’s process consists in adding milk of lime, i.e. an emulsion of quicklime with water, to the water in the reservoir on a large scale. By this means calcium carbonate is precipitated, but no effect is produced on calcium and magnesium sulphates and chlorides. The hardness of the Thames water can thus be reduced from 16° to 3° or 4° (Clarke’s scale). The calcium carbonate carries down with it suspended and possibly dissolved organic matter. In the Porter-Clarke process lime-water, i.e. milk of lime diluted, and the excess of lime separated by settlement or filtration, is mixed with the water to be purified, the water being freed from the precipitated calcium carbonate either by subsidence or by being forced through a filter of stretched canvas.
(2) Carbonate of Soda added to boiling water throws down calcium carbonate, and possibly lead if present. Much less is required when added to boiling than to cold water. Maignen’s process consists in adding anti-calcaire powder, containing chiefly carbonate of soda, lime, and alum.
(3) Aluminous salts are very effectual in removing suspended organic matter, if the water contains calcium carbonate. On the addition of alum, calcium sulphate and aluminium hydrate are formed, both of which fall to the bottom, carrying with them other impurities. The amount of alum required is about 6 grains per gallon of water. If the water is not hard, a little calcium chloride and carbonate of soda should be put in before the alum is added, in order that a precipitable substance may be formed.
(4) Potassium permanganate readily removes the offensive smell of stagnant water, but it gives a yellow tint to the water. The addition of a little alum will help to carry down the decomposed permanganate.
(5) Perchloride of Iron, in the proportion of 2½ grains to a gallon of water, has been found to completely purify water from finely suspended organic matters and clay.
(6) More recently, other substances, such as iodine and hyposulphite of soda, have been recommended. These are supposed to act by sterilizing the water, and iodine in suitable quantities undoubtedly effects this.
Chemical processes for the purification of water, with the exception of the softening process, are not to be recommended for general use. Efficient filtration, or boiling, is safer than chemical treatment; and it would only be justifiable to trust to the latter, when, as in a military campaign, an attempt at purification was necessary, and no means were available for filtering or boiling water.
7. Filtration.—The object of filtration is to remove the impurities of water. The most dangerous impurities are suspended in it, especially the microbes causing infectious diseases. Hence the most perfect filter is the one which most completely prevents the passage through it of microbes. If the water supply is pure, domestic filtration is not only useless, but likely to do more harm than good. This is true for such upland surface waters as those supplied to Liverpool, Glasgow, and Manchester; for such deep well-water supplies as those of Brighton (deep chalk), of Nottingham (new red sandstone), and others, when pumped from wells remote from inhabited houses. For upland surface waters known to attack lead pipes, filtration through charcoal or spongy iron may be advisable; for river water, filtration through a germ-proof filter is best.
Filtration on a large scale is generally carried on as follows:—A preliminary step consists in collecting the water into settling reservoirs, wherein the more bulky substances subside. The water is then filtered through beds of gravel and sand, containing perforated tubular drains below, into which the filtered water flows. The drains are covered by a bed of gravel about 3 feet deep, over which is spread a layer of sand about 1½ to 2 feet deep. Sharp angular particles of sand are the best; and the gravel should gradually increase in its coarseness as it descends.
The effect of this filtration is chiefly mechanical; it separates any suspended matter, whether organic or inorganic. A certain amount of biological action possibly also takes place. Piefke found that a perfectly cleaned and sterilised filter when first used, increases the microbes in water, instead of decreasing them. Gradually a gelatinous layer of slimy matter is formed on the top of the sand; the water now filters through much more slowly, but it gradually becomes freer from microbes, these being intercepted by the slimy layer. It is important that this layer should not be disturbed by too rapid or forced filtration, and that when the surface layer requires to be removed, because the filter has become impervious, time should be allowed for another thin film to form before the filtered water is again utilised. Koch concluded that the rapidity of filtration should never be allowed to exceed 100 millimetres (about 4 inches) per hour; and that the number of microbes per c.c. in the filtered water should never exceed 100. Some oxidation of organic matter, as well as detention of microbes, may take place during the filtration of water, nitrates being formed by the vital activity of certain “nitrifying” microbes in the filter. (On nitrification, see pages 195 and 274.) P. Frankland’s observations show that the number of microbes in Thames water is reduced by filtration through sand and gravel beds, as practised by the London Water Companies, so that only 3·4 per cent. of those originally present remained. He also concludes that the majority of the microbes present in filtered water are derived from post-filtration sources. Thus the number is greater in tap-water than in water derived from near the reservoirs.
Other materials besides sand have been used for filtration on a large scale, but none with proved success.
Domestic Filtration ought, as already explained, not to be needed, but circumstances often arise in which the public supply is open to suspicion, and a second domestic line of defence against infection through the water supply is desirable. When this is so, the form of filter which will best protect the household is one attached to the house-tap, so that all drinking-water is perforce filtered. When filtering involves the transfer of water from the tap to the interior of the filter, opportunity is left for carelessness or forgetfulness. The one essential point of a domestic filter is that it will prevent the passage through it of microbes. Every filter must be tested from this standpoint.
On this point the experiments of Woodhead and Cartwright Wood are conclusive. They first of all experimented on various filters with fine artificial ultramarine containing particles 16 µ to 0·6 µ or even less in diameter in suspension; and milk containing granules and globules of fat 0·5 µ to 30 µ or more in diameter, freely diluted with water.
| TIME IN MINUTES REQUIRED FOR FILTRATION OF 1 PINT OF WATER. | PRESENCE OR ABSENCE OF ULTRAMARINE IN FILTRATE. | PRESENCE OR ABSENCE OF MILK IN FILTRATE | |
|---|---|---|---|
| Silicated carbon filter | 68 | ++ | +++ |
| Carbon filter | 18 | + | +++ |
| Maignen’s Filtre Rapide | 4 | 0 | ++ |
| Spongy iron filter | 14 | 0 | +++ |
| Pasteur-Chamberland filter | 420 | 0 | 0 |
| Berkefeld filter | 140 | 0 | 0 |
The number + indicates the relative amount of the experimental substances that made their way through the filtering medium.
Experiments were then made with the actual microbes of certain infectious diseases, and it was found that certain filters allow these to pass. Thus a silicated carbon filter allowed 1,000 out of 15,000 typhoid bacilli suspended in water to pass through its substance; a manganous carbon filter allowed 600 to 800 out of 10,000 cholera vibrios to pass through; Maignen’s filter on the second day of experiment allowed 150 out of 5,000 cholera vibrios to pass through; Lipscombe’s charcoal filter experimentally only reduced typhoid bacilli from 20,000 to 5,000; the magnetic carbide filter only reduced them from 20,000 to 10,000; the spongy iron filter from 20,000 to 3,000; while, on the contrary, the Pasteur-Chamberland and the Berkefeld filter completely stopped all microbes and produced a sterile water. (As to these two, see page [98].)
Of the materials enumerated animal charcoal was formerly regarded as an excellent filtering medium. It is capable of oxidising organic matter dissolved in water, but so far from sterilizing water, it favours the growth of microbes in it. Water filtered through charcoal, after the first few days of use of the charcoal, deteriorates, as the charcoal yields up impurities to it.
Manganous Carbon consists of animal charcoal and black oxide of manganese mixed with oil, and heated strongly together out of contact with the air. The oxidising power of the carbon is said to be thus greatly increased. It shares the objections to carbon.
Silicated Carbon consists of 75 per cent. of charcoal and 22 per cent. of silica, with a little oxide of iron and alumina. It is not an efficient filtering medium.
Spongy iron is prepared by the reduction of hæmatite ore with fusion, so that the iron is obtained in a porous and finely-divided condition. The Rivers Pollution Commissioners found spongy iron to be “a very active agent, not only in removing organic matter from water, but also in materially reducing its hardness, and otherwise altering its character.” It is a powerful oxidising agent, some of the water being decomposed, and hydrogen set free, and the oxygen acting upon any organic matter present. It also removes lead from water. As already seen, it does not, however, fulfil the primary object of water, by depriving it of any microbes contained in it.
Magnetic carbide of iron is obtained by heating hæmatite ore with sawdust. Its action is similar to that of spongy iron.
The Pasteur-Chamberland filter consists of a cylinder of unglazed fine porcelain made from a well-baked Kaolin of a certain degree of porosity and hardness. (Fig. 10.)
The water passes through the porcelain from without inwards, and with the pressure of 1½ to 2½ atmospheres which is usually present in the pipes of a water-service, passes through at the rate of about three quarts per hour. The filter can easily be cleaned by brushing it in a stream of hot water, or by subjecting to the heat of a Bunsen burner. The filtration is entirely mechanical, the filtered water being quite freed of microbes. No chemical action takes place.
Fig. 10.
Pasteur-Chamberland Filter.
A.—Outlet of filtered water. B.—Pasteur tube. C.—Metal tube containing unfiltered water. D.—Unfiltered water delivered through tap.
The Berkefeld filter is cylindrical like the Pasteur-Chamberland filter, and is used in the same way. It is made of infusorial earth, which is soft and friable and liable to break. The cylinder becomes gradually worn thin by cleaning, and it then ceases to filter efficiently. Its sole advantage over the Pasteur-Chamberland filter is the more rapid rate of filtration; and against this is to be set the greater liability to fracture and the lack of continuance of efficient filtration. Woodhead and Wood in the report already quoted, state: “The Berkefeld filter appears to have the largest pores among the efficient filters, as is evidenced by the fact that the water organisms were not apparently weakened, that more species of organisms appeared in its filtrate, and that lowering the temperature to 11° C. did not prevent their appearance. The Pasteur-Chamberland filter, on the other hand, at 11° C. was able to give an apparently sterile filtrate for a prolonged period.” More recent experiments have shewn that pathogenic (disease-producing) microbes contained in water after awhile grow through the substance of a Berkefeld filter, and that this does not happen with a Pasteur-Chamberland filter. The latter is therefore preferable.
In determining the number of bougies required for any filter to secure a given amount of pure water, it is necessary to calculate on the basis of the output after several weeks’ use, not on the original output. If this is done, pure water will be secured without disappointment as to the amount supplied.
[CHAPTER XIV.]
COMPOSITION AND PROPERTIES OF AIR.
An abundant supply of fresh air is necessary at all times. And yet its importance is commonly ignored in practical life. Strenuous efforts are made to ensure a supply of food, and water is commonly filtered or otherwise purified before drinking; but many are content to live in an impure atmosphere, which hardly suffices for the preservation of life, and certainly not of health. Deprivation of food, or even of water, only kills after several days or weeks; deprivation of air kills in a few minutes. Only about three pints of water are required daily, while at least 1,500 gallons of air are necessary every day for carrying on the vital functions.
Composition of Air.—The air constitutes a gaseous ocean in which we live, as fishes live in water. In virtue of its weight, it exerts a pressure of about 15 lbs. on every square inch. This pressure is usually measured by the barometer, and is equivalent on an average to that of a column of 30 inches of quicksilver. (See page [331]).
Chemically, air consists of a mixture of various gases and vapours. These are chiefly Oxygen and Nitrogen; but in addition, there are minute quantities of carbonic acid, argon, hydrogen, water vapour, ammonia, ozone, and suspended matters.
The oxygen and nitrogen exist, in the proportion by volume of 20·9 of oxygen to 79·1 of nitrogen, or of 23·16 grains of oxygen to 76·84 of nitrogen, by weight.
These two gases do not exist in chemical combination, but mechanically mixed. This is proved by the fact, that they do not exist in air in the proportion of their combining weights, or any multiple of these; that the proportion varies slightly at different parts; and that the air which is dissolved in water does not contain the nitrogen and oxygen in the proportion 4 to 1 (as in the atmosphere), but in the proportion 1·87 to 1. This means that oxygen, being more soluble in water than nitrogen, has dissolved in a larger proportion; as it certainly would not have done, had the oxygen and nitrogen been chemically combined. The oxygen dissolved in water supplies fishes with the necessary oxygen for their respiratory processes. Similarly the oxygen in the atmosphere is its most essential constituent, being required in all processes of oxidation (i.e., combustion), whether in living organisms or in the inanimate world. Nitrogen serves as a diluting agent. It is incapable of supporting life alone; and many of the fatal accidents which have occurred through men descending deep wells without first testing, by means of a lit candle held well below them, the quality of the air near the bottom, have been due to an accumulation of nitrogen in the well.
Ozone is a condensed form of oxygen, which is present in minute quantities in pure air, and especially during a thunder-storm or after a fall of snow, and in the air near the sea. In it three volumes of oxygen are condensed so as to occupy two volumes. In this condensed condition it has powerful chemical affinities; often oxidising substances which oxygen cannot attack. It is generally absent from the close air of towns and dwelling houses, having been used up to oxidise the organic matter present in these places. Air without it is said to be “devitalised”; and ozone has been described as the scavenger of the air.
Ozone can be produced by hanging a piece of moist phosphorus in a room; and it is stated by Dr. Daubeny, that part of the oxygen given out by plants, especially by scented flowering plants, is in the condition of ozone. A small quantity is produced when an electrical machine is worked; its presence is evidenced by a peculiar smell (the name ozone is derived from the Greek word for smell).
Test of Ozone in Air.—Traces of ozone in air are detected by exposing strips of blotting paper moistened with a mixture of a solution of potassic iodide and starch. If ozone is present, the paper assumes a blue tint, due to the liberation of iodine, and its combination with the starch. Other acid gases may, however, produce the same effect. A second test should, therefore, be tried. Soak red litmus paper with a very dilute solution of potassic iodide, and expose as before. Potassic oxide is produced if ozone is present, and this turns the litmus blue.
Aqueous Vapour is always present in air, though the amount varies greatly. It is invisible in the ordinary condition, but by condensation becomes cloud or fog, rain, snow, or hail. The quantity of moisture present varies with the temperature of the air; the higher the temperature, the more water can be vaporised, without the point of saturation being reached. An increase of 27° Fahr. doubles the capacity of air for moisture. The amount of moisture that would saturate air at 50° Fahr. only gives 71 per cent. of the saturation amount at 60° Fahr. The amount of moisture is estimated by the hygrometer (page [240]).
Air saturated with moisture at 32° Fahr., holds vapour equal to 1 ∕ 160 of its weight; at 59° it holds 1 ∕ 80, at 86° 1 ∕ 40, at 113° 1 ∕ 20, and at 140° 1 ∕ 10.
Ammonia in normal air does not exceed one part in a million of air; but it is always present—either as free ammonia or as sulphate, chloride, carbonate, or sulphide of ammonia. From this source, plants derive some of the nitrogen they require as food; some also from the free nitrogen, which is fixed by certain microbes, growing in the nodules connected with the roots of peas, lentils, and other plants (page [274]).
Traces of nitrous and nitric acid are also present in the air, produced by the direct combination of nitrogen and oxygen occurring as the result of the electric spark during lightning.
Carbonic Acid or carbon dioxide is always present in air, in the proportion of 3·36 to 4 parts in 10,000; but in impure air may be present in much larger amount. It is a heavy gas, incapable of supporting combustion, and therefore of supporting animal life. Being a heavy gas, it tends to accumulate where it is produced, as about lime-kilns by the heating of chalk. Thus CaCO₃ (chalk) (heated) = CaO (lime) + CO₂ (carbonic acid). Tramps have occasionally died of carbonic acid poisoning through sleeping near lime-kilns.
It is produced by the oxidation of carbonaceous matters, hence in all ordinary combustion, in many cases of putrefaction and fermentation, and in the respiratory processes of all animals.
Plants diminish the amount of carbonic acid in the atmosphere. Two processes occur in most plants: a process of respiration, as in animals; and a process of assimilation, by which the leaves and all other green parts of a plant under the influence of sunlight decompose the carbonic acid of the atmosphere, fixing its carbon and liberating its oxygen. Plants such as fungi, which are destitute of green colouring matter, cannot decompose carbonic acid; nor can any plants during the night. During the day green plants are air purifiers; during the night all plants vitiate the air to a slight extent.
The Air in Relation to Respiration.—The oxygen of air is absolutely essential for the continuance of life. In every organised animal, lungs or analogous organs are provided, in order to supply the necessary oxygen to the system, and to remove the impure air from it.
The act of breathing occurs in man about seventeen times per minute. While the inspired air is in contact with the interior of the lungs, it undergoes important alterations. It comes into contact with the five or six millions air-vesicles which form the minute dilated terminations of the windpipe, and have an aggregate area of ten to twenty square feet. Each of the air-vesicles has extremely thin walls; and outside these delicate walls lie capillary blood-vessels, full of impure blood. An active interchange now occurs between the air and the gases dissolved in the blood. Oxygen passes through the intervening membrane into the blood, while carbonic acid and other impurities of the blood pass into the air-vesicle. The consequence of this is that the impure dark-coloured blood becomes bright scarlet and pure. This purification is not confined to any one portion of the blood; for the heart contracting 60 or 70 times per minute, pours successive portions of blood into the capillaries surrounding the air-vesicles; while at the same time, pure air is brought into the air-vesicles seventeen times per minute, and so the interchange is constantly kept up.
In view of the incessant character of respiration and circulation, it is clear that all the blood will be purified if the external air is pure; and that if there is any detrimental matter in the air, it probably will come into contact with the blood in the lungs.
The amount of air taken in with each inspiration is about thirty cubic inches. This is called the tidal air, as it is constantly ebbing and flowing from and to the lungs. By means of a very forced inspiration, about 100 cubic inches of additional air can be inspired; and similarly after an ordinary inspiration, one can expire forcibly an additional 100 cubic inches, though there will still be left in the lungs another 100 cubic inches of air. Thus:—
| Tidal air | 30 | cub. in. |
| Complemental air | 100 | „ |
| Supplemental air | 100 | „ |
| Residual air | 100 | „ |
| —— | ||
| Total capacity of lungs | 330 | „ |
Corresponding to the respiratory changes in the lungs, there are changes in the tissues throughout the body. The pure and oxygenated blood leaving the lungs, is carried to all parts of the system. Oxidation and allied processes are actively carried on, the result of which is the formation of urea, carbonic acid, and smaller quantities of other effete matters. These are then carried by the blood to the excretory organs, urea being chiefly eliminated by the kidneys, and carbonic acid by the lungs.
Examination of Expired Air shows that—1. It is heated; in its passage through the nose and deeper respiratory passages it has acquired a temperature approaching that of the blood.
2. Its moisture is increased. By the skin and lungs from 25 to 40 ounces of water pass off in the twenty-four hours; the relative amount varies somewhat.
3. It contains 4 to 5 per cent. less oxygen, and 4 per cent. more carbonic acid than inspired air. The carbonic acid, instead of being 4 parts in 10,000 of air, becomes over 400 in 10,000, while the oxygen is diminished in a somewhat larger proportion. Thus:—
| OXYGEN. | NITROGEN. | CARBONIC ACID. | |
| Inspired air contains | 20·81 | 79·15 | ·04 |
| Expired air contains | 16·033 | 79·557 | 4·38 |
The amount of carbonic acid expired varies under different circumstances. It is increased by active work, by an increase of food, by a diminution of the external temperature; it is greater when the surrounding air is pure, and when it is moist; and it varies with the season, being greatest in spring, and least in autumn.
Children require more oxygen, and expire more carbonic acid than adults, weight for weight. A child six or seven years old requires nearly as much oxygen as one twice that age. Boys usually require more air than girls, as they are more active and exhale a larger amount of carbonic acid and other impurities.
The average amount of carbonic acid eliminated by a healthy adult is at least 0·6 cubic foot per hour, or 14·4 cubic feet per day. This reckoned as carbon is equivalent to 160 grains per hour, or half a pound of carbon in the twenty-four hours. Liebig gives the amount of carbonic acid expired as 0·79 cubic foot per hour, or 19 cubic feet per day.
4. It contains organic impurities. These are chiefly gaseous, solid particles only being expired during coughing, or possibly during conversation. The danger from the “breath” of patients in infectious diseases is really associated rather with the dried discharges on handkerchiefs, etc., than from the “breath” itself; unless droplets of saliva discharged during speaking, or mucus during coughing, are directly inhaled.
[CHAPTER XV.]
SUSPENDED IMPURITIES OF AIR.
Pure air being essential to life and health, it is important to ascertain the character and origin of the impurities of air. Innumerable substance—in the condition of gases, vapours, or solid particles—constantly pass into it, and deteriorate its quality. To counteract this, certain purifying agencies are at work, the mechanism of which will be considered hereafter.
Impurities are much commoner and more abundant in the air of enclosed spaces than in the external air, as the natural processes of purification cannot be brought to bear so efficiently in the former case. In sick rooms, hospitals, etc., impurities arise, which are not present where only healthy people are collected. The most important impurities are derived from the respiration of animals, and the combustion of gases, candles, or lamps in rooms, from sewage emanations, from various occupations, and the air of marshes, mines, church-yards, etc. These may be classed under two heads—solid and gaseous; the solid being simply suspended in the air in a finely divided condition, or floated about in a coarser condition by currents of air. They are revealed in an atmosphere in which one did not previously suspect their existence, by the passage of a beam of sunlight. Light itself is invisible, but its course is rendered visible by the particles from which its rays are reflected. Tyndall demonstrated the presence of minute particulate matter in the air of all ordinary situations, and showed that a large proportion of this matter consists of germs (microbes). In his experiments with vapours in closed tubes, floating matter was always revealed by a concentrated beam of light, even though the air entering the tube had been first drawn through sulphuric acid and through a strong solution of caustic potash. If this air was then passed through a red-hot platinum tube and across folds of red-hot platinum gauze, it became optically empty; the floating matter had been burnt, and disappeared. It was therefore organic. In subsequent experiments, he took organic solutions, as of meat, turnip, and the like, and rendered them sterile by repeated boiling. They remained sterile when kept in air-tight vessels or in vessels covered with a thick layer of cotton-wool, which would efficiently filter any entering air; but when exposed to the air, they invariably became turbid, owing to an enormous multiplication of germs. Clearly, therefore, air contains organic, matter, and much of this organic matter consists of living germs. Most of these germs are comparatively harmless under ordinary conditions. They are, however, the causes of fermentation, putrefaction, and all the processes of decomposition which occur in organic substances. The importance of the exclusion of the dust of air has received an important application in Lister’s antiseptic and in the aseptic system of treatment of wounds. Formerly accidents and operations were frequently fatal; now vast numbers of lives are saved by improved surgical methods. The original antiseptic method acted on the supposition that some germicidal application to the wounds was necessary; now it is realized that if, during the operation, germs are not allowed to remain in the wound, all that is afterwards necessary to insure rapid recovery is that they shall be prevented from entering the wound from the external air during its process of recovery. By the adoption of such means, large wounds can be made to heal, without the formation of a drop of “pus” or “matter.” (See also page [110].)
Suspended Matters are mineral or organic, the two being commonly associated together. The mineral matters consist largely of fine particles of common salt, silica, clay, iron rust, dried mud, chalk, coal, soot, and similar substances. Not uncommonly the mineral particles are coated by, or mixed with, organic matter, the comparative lightness of the organic matter enabling the mineral matter to float about more easily. The objection to dust is thus intensified, for not only is it irritating to the respiratory passages and generally disagreeable, but it carries with it putrescent and possibly morbific particles. The prevention of infectious diseases resolves itself largely into means for preventing the inhalation of dust.
Organic Suspended Matters in the open air are, most commonly, minute fragments of wood and straw, dried horse litter, fragments of insects, the spores and pollen of plants, and microscopic plants and animals. In addition, there is the putrescent organic matter resulting from respiration and other organic functions.
Indoors, the air commonly contains, in addition, fragments of cotton, linen, silk, or other fibres, fragments of vegetables, starch cells, soot, charred wood, splinters from floors, etc.
In Sick Rooms, products of the morbid conditions may be evolved; thus, pus-cells, particles from the expectoration, blood cells, fat particles, epithelium, or the special germs or microbes to which infectious diseases are due. These are disturbed by the movements of persons, causing the dust to rise; and thus the infection of consumption, and of the acute infectious diseases, is frequently spread.
Flies and other winged insects are important auxiliaries in the diffusion of disease-carrying particles. Receiving some morbid secretions on their limbs, or other parts of their bodies, they have occasionally been the means of spreading erysipelas in hospitals, and glanders in veterinary stables. The specific contagia of cholera, enteric fever, and summer diarrhœa are occasionally conveyed to food by flies which have previously alighted on latrines or privies or other places where the stools of such patients have been deposited (page [281]). The excreta of flies, which are not uncommonly deposited on food, or on articles of furniture, have occasionally being found to contain the minute ova of intestinal worms.
Effects of Suspended Matters.—The inhalation of dust is followed by deleterious effects. We may divide the solid substances inhaled as dust into three kinds:—dead substances, living substances, and the contagia (microbes or germs) of various diseases.
1. Dead Substances inhaled for a prolonged period in various occupations are a common cause of premature death. The potter draws into his lungs a fine silicious dust, which irritates his lungs, and finally produces a fatal disease, known as potter’s asthma.
Mill-stone Cutters and Stone Masons inhale the fine particles of stone given off from the material which is being chiselled. These produce serious disease of the lungs.
Pearl Cutters inhale fine particles of pearl-dust, and as they generally work in close rooms, and the dust is light and tasteless, serious disease of the lungs results.
Sand-paper Makers inhale minute portions of glass and sand; and needle and knife grinders are exposed to similar dangers, and at one time the mortality among them was frightful. It has greatly diminished since the introduction of wet grinding, the use of steam fans, and wearing of respirators.
Hemp and Flax Dressers inhale a dust which is peculiarly irritating. Workers in rags and in wool suffer in like manner from dust. The dust from fleeces of wool, and especially from the alpaca fleece, has produced in many cases (in the neighbourhood of Bradford and elsewhere) an acute disease (anthrax) proving fatal in a few days. The spores of this disease are very persistent of life (page [274]), and remain active for mischief for months after the death of the animal which had suffered from it. The fleece can be disinfected by steam; and the use of fans for diverting the dust created during “sorting” minimises the danger from it.
The miller commonly suffers from a form of asthma, not so severe as potter’s asthma, as the particles in this case are not equally irritating. The hairdresser is liable to inhale the short fragments of hair cut by the scissors, and the mortality of this class of workers is high. Miners in coal have a surprisingly low mortality, when accidents are excluded from the calculation; except in South Wales, where it is slightly higher than for all males in the same district. Coal dust is relatively free from sharp angles, and is therefore not so irritating to the lungs as metallic dust. Consumption is relatively rare among miners.
The Fur-dyer is very prone to suffer from the dust of the dyed furs, great irritation and disease resulting in many cases.
Artificial Flower-makers, and those engaged in colouring arsenical wall-papers, suffer from the inhalation of arsenical vapours, as well as from the irritating effects of its absorption by the skin. These are now seldom seen, owing to the almost complete abandonment of the use of arsenic for wall-pigments.
Cigar-makers are liable to have their lungs irritated by inhalation of the dust of the tobacco-leaf; and may suffer from tobacco-poisoning.
Workers in Lead are very liable to be poisoned by the metal, e.g., house painters, potters engaged in the glazing process, in which the ware is dipped into a solution containing lead, manufacturers of white lead, and others. The lead is partly absorbed by the skin; in some cases it is inhaled as dust; and more often it is swallowed, when the workman eats his meals with unwashed hands. Of the symptoms “painter’s colic” and “drop-wrist” are the two most important, though, in some cases, lead shews its effects more insidiously, leading to gout and chronic renal disease. It is now compulsory on employers to provide in the workshop, complete washing arrangements for the use of workers in lead. Every doctor called to attend a case of lead or phosphorus or arsenic poisoning or anthrax, which has been acquired in an industrial occupation, must notify the same to H.M. Inspector of Factories. This implies inspection of the factory or workshop and the subsequent adoption of further measures of precaution.
Brass-founders occasionally inhale the fumes of oxide of zinc; and diarrhœa, cramp, waterbrash, and other troubles are the result. Those engaged in the manufacture of bichromate of potass, are liable to partial destruction of the mucous membrane of the nose, and to irritation of the skin, with the formation, in some cases, of small ulcers.
Workers with Phosphorus, as those engaged in the making of phosphorus matches, not uncommonly suffer from a gradual necrosis (death) of the jaw-bone. Those having carious teeth are especially attacked by this disease, which is due to the fumes of oxide of phosphorus, attacking the jaw. Improved ventilation of workshops, careful attention to the teeth, and other measures, have greatly diminished this disease; and it has disappeared where safety matches made from red non-volatile phosphorus, have replaced matches made from the yellow variety.
Chimney Sweeps occasionally suffer from irritative skin diseases, as well as bronchitis. In some cases the chronic irritation of the soot has produced cancer of the skin.
The effect of dust on workers can be seen in the mortality returns: Among men aged 25 to 65 years in 1881-90, the comparative mortality figure in England and Wales was as follows, all males throughout the country being taken as a standard and given as 1,000:—
Comparative Mortality Figures.
| All males | 1000 | ||
| OCCUPATIONS WITH NO DUST. | DUSTY OCCUPATIONS. | ||
| Clergyman | 533 | Coal miner (Derby and Notts.) | 727 |
| Gardener | 553 | Carpenter | 783 |
| Farmer | 563 | Bricklayer, mason | 1,001 |
| Teacher | 604 | Coal miner (Lanc.) | 1,069 |
| Tool and scissors maker | 1,412 | ||
| Potter | 1,706 | ||
| File-maker | 1,810 | ||
Remedial Measures.—Means have been taken to diminish the prevalence of the above dust diseases, in several cases with remarkable success. In the case of steel-grinding, for instance, the mortality is greatest with dry grinding, and least with wet grinding. Wet processes have been applied to others of the industries named, with a like success. Where the dust cannot be avoided, the use of steam or electric fans, to deflect the dust away from the workman, has been found successful; and in many cases, free ventilation of the workshops has greatly diminished the mortality. Where none of the above measures suffice, the use of respirators ought to be insisted on. Breathing through the nostrils ought to be carefully maintained, as thus the dust is to a large extent stopped before reaching the lungs.
The dangers of lead poisoning may be avoided by absolute cleanliness, the hands being always washed before taking meals, and the nail-brush used to secure complete cleanliness beneath the nails.
2. Living Substances.—The pollen of plants in some persons produces a distressing form of disease, called hay-asthma, which is apt to recur each year, and is sometimes only curable by living in a town or removing to the sea-coast. The amount of pollen floating about in the atmosphere is considerable; 95 per cent. of it is grass-pollen, and this form and the pollen from pine-trees appear to be the most powerful in inducing hay-asthma. According to some authorities, hay-asthma is rather due to the minute particles constituting the scent of various flowers, than to the pollen; but that is probably not the usual mode of origin of the disease, though it may be in some cases. In some cases, true asthma results from smelling particular plants. Here as in the case of hay-asthma a peculiar idiosyncrasy is involved, only a very small proportion of those exposed to the minute particles suffering from asthma.
The spores of many fungi and of other living organisms are constantly being floated about in the air, until they find a suitable resting place, when they settle and proceed to grow and multiply. The souring of milk, the fermentation of a saccharine solution, the moulding of bread, the presence of mildew, the blighting of corn, and numerous other phenomena are due to the growth of organisms carried by the atmosphere from one part to another.
3. The Contagia (microbes or germs) of the acute infectious diseases are minute living organisms, known as bacteria. Hence these diseases may be carried about by currents of air, some much more easily than others. Some of the contagia have a persistent vitality. Thus the contagia of scarlet fever, diphtheria, or small-pox may infect a room for months, causing the disease in question, when infected articles in the room are disturbed. The contagia of typhus fever and of measles, on the other hand, are short-lived, and do not usually resist free ventilation and exposure to sunlight.
Besides the contagia of the acute fevers, septic organisms may be carried by the atmosphere. Formerly, blood-poisoning from operation and other wounds was common; but Lister, by insisting on absolute cleanliness of wounds, and only allowing air to have access to the wound which had been filtered through layers of gauze and deprived of its septic germs, has secured that wounds can now be kept perfectly “sweet,” the suppuration in them reduced to a minimum, and the danger of blood-poisoning almost annihilated (page [106]). It had often been noticed that recovery from even very severe injuries was common, if only the skin remained unbroken; while the same injuries, with the addition of a rupture of the skin, and consequent access of air, were rapidly fatal. But to Lister is due the great honour of proving that it was not the air which produced the mischief, but the germs it contained, and that filtered air might be admitted with impunity.
Erysipelas and hospital gangrene have occasionally been carried about in hospital wards by dirty sponges and dressings; and if the ventilation is not perfect, particles of epithelium and pus from diseased persons may be carried to other patients at a distance. Some forms of purulent disease of the eyes are transferable from patient to patient, and in children some forms of eczema are also contagious.
[CHAPTER XVI.]
GASEOUS AND OTHER IMPURITIES OF AIR.
Gaseous impurities of the air are very commonly associated with suspended matters, and it is often difficult to separate the effects of the two.
Different gases are also often associated, and so produce modified results. It will be convenient to consider, first of all, certain well-marked gaseous impurities, and then others in which there is a mixture of several gases, or of these with suspended solid particles.
Under the first head the most important impurity is—
(1) Carbonic Acid.—This is reckoned an impurity if amounting to more than 5 parts in 10,000 of air. Owing to the large amount produced in the respiration of animals, in the combustion of fires, gas, lamps, etc., and in other natural processes, it would be much greater in populous parts, were it not for the rapid diffusion occurring in the air, and the purifying action of plants. The following analyses (Angus Smith) illustrate the facts that in towns the amount rises, and is greatest in the most populous parts, while during fogs it is greatly increased.
| VOLUMES OF CARBONIC ACID IN 10,000 VOLUMES OF AIR. | |
|---|---|
| On the mountains and moors of Scotland—mean of 57 analyses | 3·36 |
| In the streets of Glasgow—mean of 42 analyses | 5·02 |
| London, N., N.E., and N.W. postal districts—mean of 30 analyses | 4·384 |
| London, E. and E.C.—mean of 12 analyses | 4·745 |
| Manchester streets, ordinary weather | 4·03 |
| During fogs in Manchester | 6·79 |
The effects of carbonic acid gas alone must be carefully distinguished from those of the same gas plus the organic impurities from respiration, with which it is commonly associated. Dr. Angus Smith found that air containing 3 per cent. of carbonic acid produced difficulty of breathing, but he was able to breathe comfortably an atmosphere containing 0·2 per cent. carbonic acid. Other observers have found they could breathe without discomfort air containing 1 per cent. carbonic acid. When the carbonic acid is derived from respiration, headache and giddiness are produced in many persons when the carbonic acid amounts to 0·15 per cent. A fatal result has occasionally occurred from the inhalation of the carbonic acid at the bottom of brewing vats, or about lime-kilns. The gaseous impurity at the bottom of wells is more commonly nitrogen than carbonic acid (page [102]).
The presence of an excess of carbonic acid diminishes the elimination of carbonic acid from the lungs, nutrition and muscular energy being consequently impaired. This is seen in workshops where the air is confined and gaslight is commonly employed; though the air here also contains carbonic oxide, sulphurous acid, and organic impurities, and these probably have a large share in producing the evil results.
(2) Carbonic Oxide in the proportion of more than 1 per cent. is rapidly fatal, and has poisoned when under ½ per cent. Poisoning by its means occurs where charcoal stoves are used, and especially when the charcoal is burnt in rooms with no chimney flue. This is an occasional mode of suicide on the continent. Carbonic oxide is a much more deadly poison than the dioxide (carbonic acid); it forms a stable compound with the hæmoglobin of the red blood-corpuscles, displacing oxygen from them, and is got rid of with great difficulty. Lace-frame makers place a coke stove under their work, and thus inhale the invisible gas. Headache, giddiness, irregular action of the heart, and depression of the general health result. Carbonic oxide is the most poisonous constituent of coal-gas, and is present in much larger quantity in carburetted water-gas with which coal-gas is now commonly mixed, than in pure coal-gas (page [115]).
(3) The inhalation of Sulphuretted Hydrogen produces headache, nausea, and diarrhœa; but in manufactures involving the inhalation of a small proportion of this gas the symptoms are much slighter.
(4) Sulphurous Acid is always present in small quantities in the air of towns, derived from the combustion of coal and coal-gas. Straw-bleachers and the bleachers in cotton and worsted manufactories, often suffer from severe cough and bronchitis due to inhaling its irritating vapours.
(5) Carbon Disulphide when vaporised and inhaled produces headache, general muscular pains, and nervous depression. It is used in the manufacture of waterproof coats, toy balloons, etc.
(6) Ammonia produces irritation of the eyes and bronchial irritation. Hat-makers commonly suffer from its effects, being generally pale and feeble. It is difficult to say how much is due to the ammonia, and how much to the high temperature at which they work.
(7) Acid Fumes are very irritating to the lungs, and in the case of alkali manufactures, they destroy all vegetation for considerable distances. Hydrochloric acid produces great irritation, and chlorine even more so. The fur-dyer is not only subject to the dangers of dust, but also of the fumes of nitric acid, used to remove fat and give certain shades of colour to the fur.
(8) Other Vapours evolved in various processes produce special symptoms. House-painters suffer from the inhalation of turpentine vapour, headache and loss of appetite commonly resulting. The symptoms from the commonly coexistent lead-poisoning are distinct. Brush-makers have a persistent cough, due to the inhalation of resinous fumes, evolved in making brushes.
Workers in paraffin are liable to an irritative disease of the hair-follicles of the body, followed by the formation of scars, almost like small-pox marks.
Workers in quicksilver, as those engaged in making mirrors or thermometers, are prone to suffer from mercurial poisoning. The gums become spongy, and there is profuse salivation, also generally alimentary disturbance; and in some cases nervous affections, resulting in persistent muscular tremblings, etc.
Under the second head—cases of inhalation of mixed gaseous and particulate contamination—we must consider
(1) The Effects of Air Rendered Impure by Respiration.—It has been already stated that an amount of carbonic acid which could easily be borne alone, is intolerable when other products of respiration are mixed with it. These are chiefly organic gases and solids, which (unless removed quickly) render the atmosphere close and “stuffy”—an effect which is readily perceptible by the sense of smell of those entering an occupied room immediately from the outer air. When such a room is inhabited for a few hours, headache, langour, drowsiness, and yawning (which is really a cry for purer air) result. The soporific effects so commonly produced in churches, etc., are commonly due to the vitiated atmosphere, rather than as is supposed to the soothing effects of the sermon.
When the exposure to foul air is more chronic, and occurs day after day, there results a general lowering of strength and vigour—both bodily and mental—even where no actual disease is set up. Oxidation processes are retarded; the consequence is an anæmic sallow complexion, which compares badly with the ruddy complexion of those spending a great part of the day out of doors.
The prolonged breathing of air, foul from the products of respiration, is perhaps more common in workshops and schools than in private houses; but in both, a faint smell is commonly perceptible on entering from the open air, indicating imperfect ventilation and accumulation of organic putrescible matter. The preceding remarks are left as in the last edition. It must be noted, however, that recent research attaches more importance to the particulate matter (dust) in the atmosphere than to the amount of gaseous impurity, though the latter remains a convenient index of impurity. Experiments made by Drs. Haldane and L. Smith on themselves negative the older conclusion that a special organic poison exists in expired air. They were able without any appreciable effect on themselves to breathe air which was vitiated to such an extent as to completely prevent a match from burning; and they conclude that excess of carbonic acid and deficiency of oxygen are the sole cause of danger from breathing air highly vitiated by respiration. This conclusion may be accepted under the conditions of these experiments. Under ordinary conditions, however, the evil effects produced by breathing the air of crowded rooms, are due not only to the excess of carbonic acid and deficiency of oxygen, but also to the dust which is usually associated with them. This dust, which may be derived from handkerchiefs of patients suffering from influenza, consumption, sore throat, &c., or from other sources, is apt to be inhaled by the persons occupying such rooms.
The tendency to catarrhs is greatly increased by living in a vitiated atmosphere. In the causation of “colds” two elements are concerned, the infective agent, and the condition of the patients. “Colds” are caused primarily by infection from previous patients. The nasal discharge of a “cold in the head” contains the contagium. This is dried on handkerchiefs, and is subsequently scattered as dust, and thus conveyed to others. Ordinarily there is considerable resisting power against such catarrhs. When, however, the general vitality or the local vitality of the mucous membrane of the nose, throat, and lungs is impaired by the breathing of impure air or by sitting in wet clothes after exposure to wet and cold, a catarrh is produced.
The close connection of phthisis (consumption) with overcrowding and the breathing of a vitiated atmosphere will be discussed hereafter (page [313]). The polluted air acts in producing consumption by depressing vital functions, and diminishing the powers of resistance against the actual contagium of the disease, which is inhaled as dust, produced by the drying of the expectoration of consumptive patients.
The germs of infectious diseases are propagated very rapidly in an impure atmosphere; and typhus fever occurs almost solely in conditions of overcrowding.
In the cattle-plague of 1866, it was found that nearly all the cows died when crowded together in unventilated sheds, while only a third died when there was free ventilation.
The effects of air containing the products of respiration in a concentrated condition, and of a deficient supply of air, have been shown only too well in the oft-quoted case of the Black Hole of Calcutta. In this case, 146 persons were confined in a space eighteen feet every way, with two small windows on one side. Next morning 123 were found dead, and the remaining 23 were very ill.
In the experience of this country, the highest death-rates are in the most densely populated districts. The death-rate from phthisis, childbirth, and typhus fever for instance, is far higher in cities than in country-places. The fact may be explained in various ways. Density of population commonly implies insufficient or unwholesome food, unhealthy work, and poverty; but especially impurity of the air, uncleanliness, and imperfect removal of excreta. Of these factors, the vitiated air is probably the most powerful for evil. Children suffer more than adults from close aggregation of population, largely owing to the greater ease with which infectious diseases spread in towns.
(2) Coal-gas is obtained by the destructive distillation of coal, free from access of air. The average composition of London coal-gas is hydrogen 50 to 53, saturated hydrocarbons 33 to 66, unsaturated hydrocarbons 3·5 to 3·6, carbonic oxide 5·7 to 7·1, carbonic acid 0 to 0·6, nitrogen 2·5 to 4·1, and oxygen 0·2 to 0·3 per cent. Of these the illuminants are olefiant gas (C₂H₄) and the higher hydrocarbons. Sulphuretted hydrogen and other sulphur compounds are present in small quantities, averaging 12 grains of sulphur per 100 cubic feet of London gas.
The inhalation of coal-gas, even in small quantities, is liable to produce headache, and may lead to chronic poisoning if allowed to continue. Where the escape of gas is more extensive, as when a tap is left turned on accidentally during the night, two dangers may arise. If a light is struck in the room an explosion occurs; or persons may be poisoned in their sleep by inhalation of the gas. The most poisonous gas in coal-gas is the carbonic oxide. The chief product of the combustion of coal-gas is carbonic acid. Some sulphurous acid is also produced, which is irritating to breathe, and injurious to bookbindings, picture-frames, etc. If the flame is imperfect, as when the pressure of gas is too great, some carbonic oxide may also escape.
In recent years Carburetted water-gas has been largely mixed with coal-gas in certain districts. This is made by passing steam over heated coke. Thus
| C | + | H₂O | = | CO | + | H₂ |
| (coke) | (steam) | (carbonic oxide) | (hydrogen) |
The product is water-gas which burns with a non-luminous flame and has no smell. For illuminating purposes it is enriched with vaporised paraffin oil, which gives it a high illuminating power, and a smell rather like that of coal-gas. In some towns as much as 60 per cent. of this carburetted water-gas is mixed with 40 per cent. of coal-gas. Now as the former contains about 30 per cent. of carbonic oxide, and the latter only 7 per cent., a mixture of equal parts of the two gases would contain 18·5 per cent. of carbonic oxide, and would therefore be much more dangerous than coal-gas. This has been found to be so in actual experience of escapes of gas.
In speaking of these products of different illuminants, it is necessary to adopt a standard of light. In this country the standard has hitherto been a light known as “one-candle power” which is given by a sperm candle burning 120 grains per hour, or in V. Harcourt’s standard flame by a mixture of air and pentane (C₅H12). A good fish-tail or bat’s wing burner for coal-gas gives an illuminating power equal to 16 candles, and burns from 4 to 5 cubic feet of gas per hour. Most flat flame burners known as 4 or 5, and supposed to burn that number of cubic feet of gas per hour, really consume nearly double this amount of gas. In the following table the amount of various products produced and of vitiation of air caused by various forms of illuminants is compared, when an illumination equal to 16 candles is produced in each instance:—
| AMOUNT BURNT. | CARBONIC ACID PRODUCED. | MOISTURE PRODUCED. | OXYGEN REMOVED. | AMOUNT OF VITIATION PRODUCED STATED IN TERMS OF THE NUMBER OF ADULTS WHO WOULD CAUSE AN EQUAL VITIATION. | |
|---|---|---|---|---|---|
| Sperm candles | 1740 grains | 6·6 c.ft. | 6·6 c.ft. | 9·6 c.ft. | 11 |
| Paraffin oil | 992 „ | 4·5 „ | 3·5 „ | 6·2 „ | 7 |
| Coal gas burned in Argand burner | 4·8 c.ft. | 2·5 „ | 6·4 „ | 5·8 „ | 4 |
| Flat-flame burner | 5·5 „ | 3·5 „ | 7·4 „ | 6·5 „ | 6 |
Thus as an adult expires 0·6 cubic feet of carbonic acid per hour, it follows that the amount of carbonic acid produced in one hour by the various illuminants named in the above table, burning so as to give a light equal to 16 standard candles, varies from 4 to 11 times the amount produced by the adult. Candle and oils possess the advantage over coal-gas that no sulphurous acid is produced in combustion. If the pressure in the mains is excessive, some gas may escape through the burner unburnt or carbonic oxide may escape.
In England the flashing-point of mineral oils has been fixed at 73° Fahr. The material of which the reservoirs of lamps are composed should not be glass or other breakable material, and the wick should be contained in a small wick chamber extending nearly to the bottom of the reservoir. Only a tight fitting wick must be used.
The best illuminant for domestic purposes is incandescent electricity, in which no products of combustion are formed, and only a comparative small amount of heat is produced. Electrical illumination possesses the further advantages that there is no blackening of ceilings and no damaging of other decorations as in illumination by gas.
(3) Air Rendered Impure by Exhalations from the Sick. In addition to the ordinary impurities of occupied rooms, special impurities are produced, varying with the character of the disease. They may include infectious particles from the sick. In wards for consumptives and for diphtheria, dust in the room has been found to contain the special microbes of these diseases. Making beds, sweeping floors, &c. may help to scatter infectious dust; hence the importance of adopting means of cleansing which will not scatter dust, and of keeping sick-rooms spotlessly clean. In many diseases e.g. consumption, a patient may re-infect himself with such infectious dust, and thus diminish his own chance of recovery (see page [311]). Hospital wards can scarcely be too freely ventilated; but even more important than ventilation is the strictest cleanliness in every minute detail.
(4) The Air of Sewers, Cesspools, etc., may contain the products of decomposition of sewage, such as volatile fœtid organic matter, carbo-ammoniacal substances, sulphuretted hydrogen, carbonic acid, etc. The amount of these various products varies greatly under different circumstances, such as dilution of the sewage, ventilation of sewers, temperature, etc. The effluvia from cesspools are usually more concentrated than those from sewers. It appears fairly certain that the emanations from sewers or drains may give rise to diarrhœa and gastric disturbances, and to certain forms of sore throat, which favour the production of diphtheria. On the other hand, there is much evidence showing that the danger from sewer-emanations has been exaggerated. Carnelley and Haldane found that the air of the sewers of the Houses of Parliament and of certain sewers of Dundee was not very impure, containing a smaller number of bacteria than external air. There is reason to believe that the emanations from well-ventilated sewers, possessing a good gradient, so that the contents of the sewers are hurried away to the outfall, are free from danger. The chief source of possible danger would be the escape of the bacteria of such diseases as enteric fever or diphtheria, which had been discharged into the sewer from patients suffering from these diseases. But, in the absence of splashing, these bacteria could not escape from a liquid medium. Their escape could only occur when the sewer became dry, and the dust was carried up by rapid currents of air, a very improbable occurrence in sewers. Hence in the majority of instances sewer emanations must be freed from the accusation of producing infectious diseases. Sewer-men usually enjoy good health, and there is no excess of infectious diseases among them.
The emanations from obstructed drains or sewers may cause serious mischief, similarly to that occasionally produced by the emanations from cesspools. Under such conditions, sulphuretted hydrogen, carburetted hydrogen, and other gases are evolved, and fatal asphyxia has been caused by these. In other instances acute sewer-gas poisoning, without pneumonia, has followed.
The exhalations from cesspools or privies while cleaning them out, may produce severe disorders, which are sometimes fatal. When a drain is newly opened or sewer gas gets into a house, a less marked form of poisoning sometimes occurs, chiefly characterised by languor, headache, vomiting, and diarrhœa. In some cases there may be febrile attacks lasting a few days. Children are especially sensitive to such conditions and quickly fall into ill health.
The direct origin of acute infectious diseases from the effluvia from drains or cesspools has occasionally occurred. Leaky and choked drains under a house are especially dangerous. The subsoil becomes contaminated more and more as time goes on; foul gases are aspirated into the house, owing to its interior being warmer than the subsoil; and finally infectious matter may find its way into the house, or carried by insects or vermin, through cracks in the earth.
Diphtheria has been ascribed to emanations from drains and sewers. There is reason to believe that a non-specific form of sore throat may originate in this way; but diphtheria is generally, if not always, spread by personal infection. Diarrhœa has been occasionally ascribed to sewer-emanations. It chiefly occurs in hot weather, and is usually associated with a foul condition of the surface soil, and speedily ceases after this has been scoured by copious rain.
Enteric or typhoid fever, has been frequently ascribed to drain and sewer effluvia. It was formerly thought that putrefactive changes alone, under certain conditions of temperature, etc., would produce it, and Dr. Murchison, one of the greatest authorities on the subject, who adopted this view, proposed for enteric fever the name “pythogenic fever” (i.e. filth-produced). Isolated cases of enteric fever, occurring where there is no system of drainage, support the same view, as does also the fact that, with the adoption of drainage, the enteric mortality has steadily diminished. On the other hand, numerous cases can be quoted to show that emanations from excreta have been breathed, and sewage-contaminated water drunk, for years, without the production of a single case of enteric fever—until a case is accidentally imported. The weight of evidence is clearly on the side of the view that only emanations from the liquid or solid dejecta of previous enteric patients will produce enteric fever, and that it is the solid particles of the urine or fæces, either inhaled as dust or carried on to food by flies, &c., or mixed with food by contaminated water, &c., which cause infection. Furthermore, modern investigation shows that infection by dust is the exception in England; and that the enteric infection is usually swallowed and not inhaled, being taken in infected water or milk or other food.
(5) Effluvia from Decomposing Organic Matter.—(a) The air of marshes contains an excess of carbonic acid, marsh gas, etc., in addition to other organic matters. Malarial diseases are commonly ascribed to the inhalation of the marsh effluvia under certain conditions, though the recent proof of the part played by the mosquito in spreading malaria, puts the inhalation of such effluvia in the background as cause of this disease (page [307]). Some forms of diarrhœa and dysentery have been ascribed, with a less degree of probability, to the same cause. In this case, as in that of emanations from other organic sources, the impurities received by the air are both gaseous and particulate.
(b) The Air of Graveyards contains an excess of carbonic acid. The older intramural graveyards appear to have been a cause of illness; but modern graveyards, kept under good regulations have never been shown to cause illness.
(c) The Effluvia from Decomposing Carcases, especially of horses on the battle-field, have led to outbreaks of diarrhœa and dysentery among the soldiers.
(d) The Effluvia from Manure and Similar Manufactories do not seem to injure the workmen as a rule, but attacks of diarrhœa have been produced in the neighbourhood when the wind has wafted the effluvia towards any particular part. Sore throat, and occasionally diphtheria, have been ascribed to the inhalation of London manure taken into Essex.
(6) The Effluvia from Certain Manufacturing Processes seem to be rather nuisances than actually productive of ill health. The vapours given off by tallow-making and bone-burning processes are most disagreeable, but there is little or no positive evidence of their direct insalubrity.
The air of brickfields and cement works is peculiarly disagreeable.
The Degree of Moisture and the Temperature of air are of great importance in relation to health. Air which is unduly moist or dry, hot or cold, may be injurious apart from any foreign matters it contains.
The relative amount of moisture is of greater importance than its actual amount. An atmosphere which contains aqueous vapour up to the point of saturation is very oppressive; the normal evaporation of insensible perspiration (and with it of the organic impurities removed from the skin) is interfered with; and consequently the “oppressiveness of the day” is complained of.
An unduly hot air is generally productive of pallor and ill health, though it is difficult to know how much to ascribe to the high temperature, and how much to the commonly coexistent vitiated atmosphere. The temperature of living-rooms ought not to be over 60° to 65° Fahr., and of bedrooms not over 60° Fahr.
The devitalising influence of extreme cold is well known. Its effects are more particularly seen in young children and the very old, who require to be carefully tended during severe and long-continued cold weather. Dry, cold weather, with the temperature near the freezing point of water, and a cutting east wind prevailing, is not uncommonly described as “bracing.” This is so far from being the case, that it requires all the vital powers of the strong and healthy to resist its depressing influence, and the feeble of both extremes of age succumb.
[CHAPTER XVII.]
TRADE NUISANCES.
Many occupations are the source of considerable danger to the workers engaged in them. They are chiefly injurious by the inhalation into the lungs of some foreign agent, which produces serious local inconveniences and irritation, and may be also absorbed into the circulation and produce more remote effects.
The injurious agents may be classified under four heads:—
(1) Insoluble particles or dust.
(2) Soluble or partially soluble substances.
(3) Injurious gases or vapours.
(4) Effluvia from offensive trades.
It is evident that, as regards the effluvia named under (4), they might generally be included under the three previous heads, though it is convenient for our present purpose to keep them separate.
The occupations in which dust and soluble substances are productive of injurious effect have already been described, pages 107 to 109.
Injurious gases and vapours have received consideration on pages 111 and 112. The special offensive trades still require attention.
Offensive Trades.—The legal enactments relating to offensive trades are contained in sect. 112 of the Public Health Act, 1875, which states, any person who, after the passing of this Act, establishes within the district of an urban sanitary authority, without their consent in writing, any offensive trade, that is to say, the trade of—
- Blood boiler, or
- Bone boiler, or
- Fellmonger, or
- Soap boiler, or
- Tallow melter, or
- Tripe boiler, or
- any other noxious or offensive trade, business, or manufacture,
shall be liable to a penalty not exceeding fifty pounds in respect of the establishment thereof, and a penalty not exceeding forty shillings for every day on which the offence is continued.
These provisions can only be enforced in rural districts with the sanction of the Local Government Board.
The “other noxious or offensive trades,” in order to be brought within the operation of the section, must be analogous to those which are specially enumerated.
The most exhaustive and authoritative report on this subject is by the late Dr. Ballard, whose report is largely quoted in the following remarks.
We may consider (1) the extent to which the public is inconvenienced by various effluvium nuisances. The majority of the nuisances arise from trade processes in which animal matters are chiefly used. Among the most disgusting are the effluvia from gut-scraping, and the preparation of sausage skins and catgut, the preparation of artificial manures from “skutch” (the refuse matter of the manufacture of glue), the manufacture of some kinds of artificial manures, and the melting of some kinds of fat. Manufacturing businesses dealing with vegetable substances are often offensive, but rarely give out disgusting effluvia. The most offensive vegetable effluvia are probably those thrown off during the heating of vegetable oils, as in the boiling of linseed oil, the manufacture of palmitic acid from cotton oil or palm oil, the manufacture of some kinds of varnish, the drying of fabrics coated with such varnishes, and the burning of painted articles, such as disused meat-tins.
Occasionally offensive effluvia arise in connection with industries in which neither vegetable nor animal matters are used; as in the manufacture of sulphate or chloride of ammonia, and some other processes in which sulphuretted hydrogen is copiously evolved; and in the making of gas and the distillation of tar. The fumes from the manufacture of alkali and bleaching powder are acid and irritating, and produce very injurious effects on vegetation in the neighbourhood.
The distances to which nuisances extend vary greatly according to circumstances—as, for instance, the elevation at which the effluvia are discharged into the air. Discharge from a high chimney may relieve the immediate vicinity of the works at the partial expense of those living at a greater distance. With a damp and comparatively stagnant atmosphere, effluvia have a much greater tendency to cling about a neighbourhood.
(2) The industrial processes in which offensive effluvia are produced are classified by Dr. Ballard as follows:—
1. The keeping of animals.
2. The slaughtering of animals.
3. Other branches of industry in which animal matters or substances of animal origin are chiefly dealt with.
4. Branches of industry in which vegetable matters are chiefly dealt with.
5. Branches of industry in which mineral matters are chiefly dealt with.
6. Branches of industry in which matters of mixed origin (animal, vegetable, and mineral) are dealt with.
(3) It is important to inquire to what extent offensive trade effluvia are injurious to the public health. It is impossible to bring statistics to bear on the inquiry, as other influences, apart from occupation, can scarcely be eliminated. The term “injurious to health” is capable of a double interpretation. It might mean either serious damage to health, or the mere production of bodily discomfort or other functional disturbance by the offensive effluvia, leading by its continuance to an appreciable impairment of vigour, though not to any actual disease.
In the latter sense offensive effluvia have a deleterious effect on health. Such symptoms as loss of appetite, nausea, headache, occasionally diarrhœa, and general malaise are produced by effluvia of various kinds, but agreeing in being all offensive. “A condition of dis-ease or mal-aise is produced.”
There is little difficulty in proving bad effects on the workmen, though the invariable defence of manufacturers is an appeal to the condition of health of their workmen. The workmen only remain such so long as they are healthy, and as they become disabled they necessarily cease to rank among workmen. The decomposition of putrefying organic matters is unquestionably dangerous. The general doctrine of sanitation that filth is one of the chief factors in producing disease is certainly applicable to trade effluvia as well as to general sanitation. It has been alleged on behalf of such effluvia as chlorine sulphurous acid and tar vapours that they are useful disinfectants; but modern research has shown that disinfectants, in order to be of practical use, must be in such a concentrated condition that the air containing them is irrespirable. Probably such septic diseases as erysipelas are favoured by organic trade effluvia.
(4) The means available to prevent or minimise the nuisances arising from trade effluvia vary with the character of the processes. The general principles on which treatment must be founded depend, as Dr. Ballard points out, on a recognition of the following kinds of effluvia:—
Effluvia dependent—
1. On the accumulation of filth on or about business premises, or on its removal in an offensive condition.
2. On a generally filthy condition of the interior of buildings and premises and utensils generally.
3. On an improper mode of disposal of offensive refuse, liquid or otherwise.
4. On insufficient or careless arrangements in reception of offensive materials of the trade, or in removal of offensive products.
5. On an improper mode of storing offensive materials or products.
6. On the escape of offensive gases or vapours given off during some part of the trade processes.
It is evident that under the first two headings the proper remedy is cleanliness. Filth should be removed in impervious covered vessels, at regular intervals. Structural arrangements should be made, which will facilitate cleansing operations. Solid refuse should, as far as possible, be separated from liquid refuse, as thus putrefaction is retarded.
Under the last head important remedies are applicable. In many cases a careful selection of the materials of manufacture will form an effective remedy. Thus much of the nuisance connected with soap or candle works arises from the putrid condition of the fat collected from butchers and marine store dealers, and might be obviated by more regular and more frequent collection of the materials of manufacture. The offensive vapours arising during processes of manufacture may be intercepted before reaching the external air, and so treated that they lose their obnoxious character. Various methods of interception are adopted, according to the processes involved. Occasionally it is necessary to have the air of the entire workshop drawn by means of artificial ventilation in a special direction; usually the interception of air from special chambers suffices. When thus collected, the offensive air may be dealt with by (1) passing it through water or some other liquid capable of absorbing the offensive materials; or (2) passing it through some powder with which it has chemical affinity; or (3) if its offensive materials are capable of condensation by cold, passing them through an appropriate condensing apparatus; or (4) if the evolved matters are organic in nature, conducting them through a fire. (5) Occasionally it is sufficient to discharge the offensive gases into the air from a high chimney; and this always produces a mitigation of nuisance, as compared with discharge at a low level.
It is usually found that the adoption of one or other of these methods is directly or indirectly profitable to the offender.
Nuisances from the Keeping of Animals.—The 47th section of the Public Heath Act prohibits the keeping of pigs in towns so as to be a nuisance, and, as a general rule, it is possible to obtain a magistrate’s order, entirely prohibiting the keeping of pigs in towns. The excreta of the pig have a very offensive and penetrating odour, and however carefully kept, pigs in towns form an intolerable nuisance.
Not only is there nuisance from the accumulation of manure and dirtiness of the piggeries, but also from the storage and subsequent preparation of food. The boiling of hog-wash is often an even greater nuisance than the filth of the styes.
Cow-keeping and horse-keeping in towns are still allowed and, as compared with pig-keeping, form a small nuisance. Mews, if kept clean and well drained, need not be offensive, though it is objectionable for persons to sleep over stables. The removal of manure also constitutes a difficulty. The manure should not be allowed to accumulate in deep wet pits, but in an iron cage-work over a cement paving at or above the ground-level, thus allowing free drainage, and keeping the manure dry, and reducing ammoniacal decomposition to a minimum.
Cowsheds are generally very badly ventilated, as the cowkeeper finds that more milk is produced by the cows when the temperature of the shed is maintained at 65° or higher; and he does not see the necessity for providing artificial means of warmth. The grains which are used so largely for food are stored in a wet condition, and speedily give rise to nuisance. Cowsheds and stables should be well paved and well drained. At least 800 cubic feet should be allowed for each cow in the shed.
Cowsheds are regulated under the Dairies’, Cowsheds’, and Milkshops’ Order of the Local Government Board. This order provides for and insists on the registration of cowkeepers, dairymen, and purveyors of milk, by the local authority. It also provides that no cowshed or dairy shall be occupied as such, unless provision is made to the satisfaction of the local authority, for the lighting and ventilation, including air-space, and the cleansing, drainage, and water-supply of the same; and for the protection of the milk against infection or contamination. With the view of preventing contamination of milk, no person suffering from an infectious disorder, or having recently been in contact with a person so suffering, is allowed to milk cows or take any part in any stage of the business of a milk-seller. The milk of a cow suffering from cattle plague, pleuro-pneumonia, or foot and mouth disease must not be mixed with other milk, must not be sold or used for human food, nor for food for swine or other animals, unless it has been boiled. By the order of 1899 this regulation is made to extend to tubercular disease of the udder.
Slaughtering of Animals.—Nuisance may arise in slaughter-houses from various causes:—(1) the uncleanly way in which animals are kept in the pound or lair before being killed; (2) the insanitary condition, bad paving, lack of lime-whiting of walls, etc., of the slaughter-house; (3) the accumulation of hides, blood, fat, offal, dung, or garbage on the premises; (4) the uncleanly condition of the blood-pits, or the receptacles for garbage; (5) the flowing of blood or offal into the drains and thence into the public sewer.
Private slaughter-houses ought to be abolished, and all animals intended for human food slaughtered in public abattoirs under efficient supervision. When a large number of private slaughter-houses exist in different parts of a large town, it is impossible for the sanitary officials to properly supervise the slaughtering, or to ensure that diseased meat shall not enter the market. The inspector may only have the opportunity of examining the flesh, the internal organs which more particularly show the presence of a diseased condition having been concealed. Such concealment and the consequent foisting of diseased meat upon the public, can only be efficiently prevented by forbidding the slaughtering of any animal intended for food in a private slaughter-house.
Most local authorities have bye-laws regulating the slaughtering of animals. These provide for a cleanly condition of the lairs, and prevent keeping the animals longer in the lairs than is necessary for the purpose of preparation for slaughtering. They also insist on the provision of proper covered receptacles of iron or other non-absorbent material for the reception of garbage, and similar receptacles for blood; for cleansing of the floor, etc. after slaughtering; for lime-whiting of the walls four times a year; and for other matters of detail.
For knackers’ yards similar regulations are applicable. The flesh should not be kept until it becomes putrid before being boiled, and the boiling of the flesh and fat should be so arranged as to avoid the escape of offensive vapours into the external air.
In smoking bacon, the singeing has formed a serious nuisance. Fish-frying in small shops is often a most troublesome nuisance. A hopper over the pan in which the frying is conducted has not been always successful in carrying the fumes up the chimney. The frying should preferably be done in a closed outhouse, close to a chimney with a good up-draught.
The fellmonger prepares skins for the leather-dresser, the chief operations being taking off the wool, liming the skins, etc. The skins deprived of wool are called “pelts.” The pelts are thrown into a pit containing milk of lime, and thence sent direct to the leather-dresser. Nuisance may arise from (1) the odour of the raw skins; (2) the ammoniacal odour from the lime-painted skins hanging in the yard; (3) the emptying and cleansing of the “poke” or tank in which the hides are washed; (4) the foul condition of the waste lime taken from the exhausted lime pits; (5) the odour from the dirty unpaved yards.
The leather-dresser only deals with “pelts,” derived from sheep-skins; the tanner with bullocks’-hides. The skins brought from the fellmonger to the leather-dresser are first deprived of lime, and then soaked in a solution of dog’s dung, called “pure,” until they become soft. In winter this “pure” solution is warmed for use. The odour is very abominable, both from the “pure” tub, and from the discharge of the exhausted “pure” liquid into the drain.
At each stage of tanning nuisance may arise unless great precautions are taken, as when the hides are soaked in lime and water, when the hair is being removed, when the loose inner skin of the hide is being removed, and especially when the hides are soaked in pits containing pigeons’ or other dung. Nuisance may arise again during the passage of offensive hides through the street. Cleanliness is the great rule. If every process is carried on with due precaution, including frequent washing out of receptacles and the free use of disinfectants, little complaint need arise.
The manufacturers of glue and size boil out the gelatine from bits of hides and “fleshings” from leather dressers and tanners, from damaged “pelts,” ox or calves’ feet, horns, and other similar substances. The raw material is apt to be offensive in collection or while accumulating on the premises. The process of boiling causes offence by the effluvia from the steam. The residue remaining after the process is known as “scutch,” and this, unless frequently removed, is a most serious source of nuisance.
Prussiate of Potass is manufactured by heating carbonate of potass with refuse animal matters. In order to avoid nuisance the pot in which the boiling is done should have a pipe to conduct away the steam, first running horizontally and then vertically down to the back part of the fire.
Fat-melting and Dip-candle-making, as usually carried on, give rise to nuisance. The fat which is melted down usually comes from butchers and marine-store dealers in a rancid or even putrid condition, and it may be stored on the premises for some time before it is boiled. The vapours from the melting-vat are very offensive. They should be carried by means of a pipe down until they discharge just under the boiler-fire. The residue from the fat-melting process (known as “greaves”) requires frequent removal to avoid nuisance.
Bone-boiling, in order to extract the fat and gelatine, is most offensive, and most difficult to deal with. After boiling, the bones are apt to give off offensive smells. The vapours from the closed boiler should be condensed as far as possible in a worm condenser, and the remainder passed through a furnace fire.
In the manufacture of artificial manures nuisance is apt to arise (1) from the reception and accumulation of the raw materials, as putrid fish, putrid blood, scutch (the residue from the manufacture of glue), recently boiled bones, etc.; (2) from the preparation of the raw material for use. Thus the drying of condemned fish or meat on open kilns is very offensive; similarly the drying of sewage sludge. (3) From the process of mixing the materials of manufacture, irritant and offensive vapours being evolved, as for instance in the manufacture of manure by crushing bones, and converting into super-phosphate by the addition of sulphuric acid. (4) From the removal of the manure from the hot den, after it has been dried. When sulphuric acid is mixed with coprolites or other mineral phosphates, most irritant and offensive vapours are produced, which may be perceived in some cases at the distance of a mile.
Blood-boiling is now almost obsolete, having been replaced by albumen-making and clot-drying. Nuisance may arise from the blood collected from slaughter-houses being in a putrid state; and from the effluvia evolved during the drying process.
Gutscraping, gut-spinning, and the preparation of sausage-skins are very closely akin. In gut-scraping the putrid intestines are deprived of their interior soft parts by scraping with pieces of wood, and are then, after being cleansed, ready for sausage-skins. In gut-spinning the prepared gut is twisted into a cord. The small intestines of hogs and sheep are used for this purpose. The stench from these establishments is indescribably horrible. Extreme cleanliness is desirable. Immersion of the guts in common salt is useful; so also the use of impervious vessels, early removal of all refuse material, etc.
Brick and ballast burning are a frequent source of complaint in the neighbourhood of towns. Brick burning is conducted either in kilns or clamps. When bricks are burnt in closed kilns comparatively little nuisance arises; but when they are burnt in open clamps the effluvia are very irritating, partly owing to the fact that very commonly house refuse, containing vegetable and animal matters, is burnt with the bricks. Clamp burning should be absolutely prohibited in the neighbourhood of large towns.
In Ballast burning stiff clay is converted by the agency of heat into a brick-like material, which is of use in road-making. The clay is usually burnt in heaps, mixed with ashes and breeze from dust-bins. The process is offensive unless carried on with precautions similar to those for brick-burning.
[CHAPTER XVIII.]
THE EXAMINATION OF AIR.
There are various methods of ascertaining the quality of the air in enclosed spaces, of which not the least useful is the information furnished by the sense of smell, on entering a room from the external air. Besides the evidence given by the senses, chemical and microscopical examination of the air gives important information, while the thermometer and hydrometer ascertain the temperature and degree of moisture.
Examination by the Senses.—The dull grey haze hanging over a town, when it is viewed from a distance, indicates comparative impurity of its atmosphere, and the presence of a considerable amount of suspended matter, including smoke.
The smell of a stagnant atmosphere is a good preliminary guide to its condition. The fact that a room has been occupied for some time without efficient ventilation can be at once detected on entering a room from the external air. The sense of smell is extremely delicate; it has been estimated that the 3 ∕ 100,000,000 part of a grain of musk can be apprehended by it. But nothing is so soon dulled as the sense of smell. An atmosphere which did not appear to be unpleasant while remaining in a room, is intolerable when one returns to it after a few minutes in the open air. It is important not to confound the “closeness” perceived by the sense of smell, with the oppression due to the high temperature of a room. The two are easily distinguished (unless the two co-exist) by a reference to the thermometer, which ought always to be placed in rooms inhabited during the evening. The remedy for a close room is to allow free entry of fresh air, and not allow the fire to go down, as is so commonly done, under the impression that the closeness is due to heat.
De Chaumont has made many experiments, shewing how accurate is the information given by an acute sense of smell. Carbonic acid is destitute of odour, but as its amount is usually proportionate to that of the organic matter producing closeness, it may be taken as an index of the amount of impurity present in living rooms. De Chaumont found that the limit of smell is reached when carbonic acid amounts to 6 parts in 10,000 of air, or half as much again as in the external air. In the following extracts from his experiments, there was a close accordance between the evidence of his sense of smell and the amount of carbonic acid:—
| At | 14·80 | per 10,000 | Extremely close and unpleasant. |
| „ | 10·90 | „ | Extremely close. |
| „ | 9·62 | „ | Very close. |
| „ | 9·21 | „ | Close. |
| „ | 8·43 | „ | Not very foul. |
| „ | 8·04 | „ | Close. |
| „ | 6·58 | „ | Not very close. |
| „ | 5·68 | „ | Not close. |
He also found that humidity of the air had marked influence in rendering the smell of organic matter perceptible, even more than a rise of temperature. The sense of smell is doubtless aided in detecting impurities in the air, by the besoin de respirer, a feeling of oppression caused by the deficiency of interchange between the blood and air. The state of cleanliness of the room as well as of the persons in it influences smell; hence there may not be in particular instances exact correspondence between excess of carbonic acid and of organic matter.
Chemical Examination.—The estimation of nitrogen and oxygen in air is usually unnecessary, as these vary but little. The oxygen is, however, reduced in frequently re-breathed air. The ill effects of an often-breathed atmosphere are due not only to deficiency of oxygen, but also to the addition of carbonic acid and organic matters, rendering difficult the interchange between oxygen and the blood.
The Estimation of Carbonic Acid is of great importance, as under ordinary circumstances, its amount is a fairly exact indication of the amount of contamination in the air.
Pettenkofer’s Method.—A carefully dried glass vessel containing a gallon of water is filled with the air to be examined, by emptying the water in the room, the air of which is to be examined. Fifty cubic centimetres of clear freshly prepared baryta water are then added, and the stopper of the bottle then replaced. It is then well shaken, and afterwards allowed to stand for an hour. The carbonic acid combines with part of the baryta to form barium carbonate; and the baryta water remaining is consequently diminished in alkalinity. Given the alkalinity of the baryta water before and after the experiment, and the difference will give the amount of baryta which has combined with carbonic acid.
The alkalinity of the baryta is estimated by a standard solution of oxalic acid, of such a strength that 1 c.c. is the equivalent of 0·5 c.c. of CO₂. The indicator used in making this test is phenolphthalein, which colours baryta water red, but its colour disappears when neutralization is reached.
The following example is taken from “Pakes’ Laboratory Text Book of Hygiene,” p. 292:—
The jar is found to contain 3,950 c.c.
As 50 c.c. baryta water were run into the jar, the air experimented on = 3,950-50 = 3,900 c.c.
On titrating 25 c.c. of the original baryta water, 22·50 c.c. standard acid solution were required to neutralise it.
The baryta water in the jar required 19·35 c.c.
22·50-19·35 = 3·15 c.c. = difference of acid used.
But 1 c.c. acid = 0·5 c.c. CO₂ at 0° C. and 760 mm. of mercury.
Therefore CO₂ taken up by 25 c.c. of baryta = 3·15∕ 2 = 1·575 c.c.
As 50 c.c. were used the CO₂ absorbed by the baryta = 3·15 c.c. This was present in 3,900 c.c. of air. Therefore the CO₂ = 0·80 per cent.
Correction may be required for variations from the normal pressure of 760 mm. and normal temperature of 0° C., in accordance with ordinary rules.
In Lunge and Zeckendorf’s Method, the air to be examined is pumped through a glass bottle in which is 10 c.c. of a N ∕ 500 solution of Na₂CO₃ containing phenolphthalein as an indicator. The air is pumped by a hand pump through this solution until the phenolphthalein is decolourized. The number of times the ball of the pump has been squeezed indicates the amount of CO₂ present in accordance with a table prepared from separate experiments by Pettenkofer’s method.
Dr. Angus Smith’s plan for the estimation of carbonic acid in air is similar in principle to the last calculations. It is based on the fact that the amount of carbonic acid in a given volume of air will not render turbid a given amount of lime water, unless the carbonic acid is in excess.
Table.—To be used when the point of observation is “No precipitate.” Half an
ounce of lime water containing ·0195 gramme lime.
Air at 0° C. and 760 M. M. Barometric pressure.
| CARBONIC ACID IN THE AIR PER CENT. | VOLUME OF AIR IN CUBIC CENTIMETRES | SIZE OF BOTTLE IN CUBIC CENTIMETRES | SIZE OF BOTTLE IN OUNCES AVOIRDUPOIS. |
|---|---|---|---|
| ·03 | 571 | 584 | 20·63 |
| ·04 | 428 | 443 | 15·60 |
| ·05 | 342 | 356 | 12·58 |
| ·06 | 285 | 299 | 10·57 |
| ·07 | 245 | 259 | 9·13 |
| ·08 | 214 | 228 | 8·05 |
| ·09 | 190 | 204 | 7·21 |
| ·10 | 171 | 185 | 6·54 |
| ·11 | 156 | 170 | 6·00 |
| ·12 | 153 | 157 | 5·53 |
| ·13 | 132 | 146 | 5·15 |
| ·14 | 123 | 137 | 4·82 |
| ·15 | 114 | 128 | 4·53 |
| ·20 | 86 | 100 | 3·52 |
| ·25 | 69 | 83 | 2·92 |
| ·30 | 57 | 71 | 2·51 |
The foregoing table shows how to apply this method. The first and second columns state the ratio of carbonic acid in a quantity of air which will give no turbidity or precipitate in half an ounce of lime water; the third column gives the corresponding size of the bottle in cubic centimetres; and the fourth column gives the same in ounces. Thus different sized bottles, each containing half an ounce of lime water, will indicate with a fair degree of accuracy the ratio of carbonic acid in the air containing them, by giving no precipitate when the bottle is well shaken. For instance, if a pint bottle is used and there is no precipitate with half an ounce of lime water, it indicates that the ratio of carbonic acid does not amount to ·03 per cent.; if an eight-ounce bottle be used, and there is no precipitate, it indicates that the ratio does not amount to ·08 per cent., and so on. The air of a room ought never to contain more than six parts of carbonic acid in 10,000 of air, or ·06 per cent., i.e. a 10½ ounce bottle full of the air shaken up with half an ounce of clear lime water ought to give no precipitate.
Dr. Haldane has recently described (Journal of Hygiene, No. 1, 1901) a method of estimating CO2, which, although it appears complicated, is really both simple and convenient. For particulars, see the above Journal.
The Estimation of Organic Impurities may be accomplished approximately by drawing a definite amount of air by means of an aspirator, through a dilute solution of permanganate of potassium of known strength. The result is stated by giving the number of cubic feet of air required to decolourise .001 gramme of the permanganate in solution. Sulphuretted hydrogen, sulphurous acid, and other substances in air likewise decolourise the permanganate; these ought to be separately tested for, and allowance made.
The Estimation of Ammonia, whether free or derived from albuminoid impurities, is a matter requiring very delicate processes. It is accomplished in the same way as the estimation of ammonia in water, the air being drawn through perfectly pure distilled water, and then the analysis proceeded with as a water analysis. The mere presence of free ammonia may be determined by exposing to the air strips of filtering paper dipped in Nessler’s solution, which become brown if there is any ammonia in the air.
Microscopical Examination is required for the detection of suspended matters. These are the most potent for harm, containing sometimes the germs of infectious diseases. The suspended matters scattered throughout the air may be collected by Pouchet’s aeroscope. This consists of a small funnel drawn out to a fine point, under which a slip of glass is placed moistened with glycerine. Both funnel and glass are enclosed in an air-tight chamber, connected by tubing with an aspirator, by means of which when water is allowed to escape from it, air is drawn through the funnel and its particles impinging on the glycerine are there arrested. Glycerine may be objectionable from the foreign particles previously contained in it. Various other plans have been devised, one of which is to draw the air through a small quantity of pure distilled water and then examine a drop of it. By microscopic examination large particles can be detected. For the detection of bacteria and their spores more delicate methods are required.
The Bacteriological Examination of air is usually conducted as follows. Air is drawn through a wide glass tube (Hesse’s tube), which has been previously sterilised, and on the inner side of which liquid gelatine has been allowed to solidify. The air as it passes over the gelatine deposits any germs present in it. The entrance of any further germs is prevented by closing the tube, and it is then left to stand for two or three days. Moulds and colonies of bacteria will develop in the gelatine, and these can be counted and differentiated by their appearance and by further tests. In closed rooms the number of microbes (i.e., bacteria and moulds) ought not to be more than 20 per litre of air in excess of those in the outside air; and the ratio of bacteria to moulds ought not to exceed 30 to 1.
Examination of Temperature and Moisture.—The temperature should be observed at the point most remote from an open fire-place, and compared with the external temperature. For methods of estimating moisture, see page [240].
It may be useful to recapitulate at this point the desiderata in an inhabited room. The temperature should be 60-62° Fahr., the amount of carbonic acid should not exceed ·06 per cent. and the humidity should range between 73 and 75 per cent. of the amount required to produce saturation. The dry bulb thermometer should read 63-65° Fahr., the wet bulb 58°-61° Fahr., and the difference between the two should not be less than 4° or more than 8°.
[CHAPTER XIX.]
THE PURIFICATION OF AIR.
In addition to the artificial measures which will be discussed in the next chapter, various natural agencies are constantly at work for the removal of the impurities discussed in preceding chapters. Of these, the most important are the action of plants, the fall of rain, natural methods of ventilation, and certain natural constituents of the atmosphere.
1. Plants, by virtue of the chlorophyll contained in their green parts, absorb carbonic acid from the atmosphere, liberating oxygen in an active condition. In addition, ammonia and nitrous and nitric acids are dissolved from the air by rain-water, and assimilated by plants. During the night plants only give off carbonic acid.
2. The Fall of Rain clears the atmosphere of any solid particles contained in it, the impurities being transferred to rain-water which generally contains an appreciable amount of ammonia as well as other impurities. Rain not only washes and purifies the air, but by washing the ground, diminishes dust, and prevents its escape into the air. It is the great natural scavenger.
3. Ventilation—that is, the interchange of pure and impure air, is constantly being effected. Before entering on the details of ventilation, we must consider the physical causes at work which tend to purify the air, apart from all artificial contrivances. These are three in number—namely, diffusion, winds, and differences of temperature of masses of air.
(1) Diffusion causes the rapid mixture of gases placed together. Every gas diffuses at a certain rate—namely, inversely as the square root of its density. In any room which is not air-tight, diffusion is constantly occurring, air passing in and out at every possible point. Through chinks and openings in the carpentry-work of a room, the air diffuses rapidly. Bricks and stone commonly allow air to pass through them; diffusion occurs to a slight extent even if the wall is plastered, but very little through paper. Diffusion alone is quite insufficient to purify a room under ordinary circumstances; and solid particles including the organic matter evolved from the skin and lungs, not being gaseous, are unaffected by it. To remove these, the room must be periodically flushed with air, and washing of all dirty surfaces must be carried out.
Diffusion sometimes produces evil results, when the sanitary arrangements of a house are bad. If there is a leakage of sewage under the kitchen floor, the foul gases from it diffuse upwards; occasionally foul air diffuses from the dust-bin through the wall into the rooms of a house. These results are helped by the fact that the internal temperature of a house is commonly higher than the external.
(2) Differences of Temperature cause active movements of air. In fact winds are caused by movements between large masses of air of unequal temperature and consequently of unequal density. Light gases ascend, as familiarly illustrated by the smell of dinner perceived in bedrooms, or the smell of a cigar lit in the hall perceived in the attic. In rooms differences of temperature of the air are caused by the heat of fire, gas, and our own bodies. Currents of air result; the warmer and lighter air ascends up the chimney or towards the ceiling, while colder and denser air rushes in under the door or through the floor, etc. The lighter gases carry with them solid particles in suspension and thus tend to remove the most important impurities. Assuming that the external air is colder, if admitted into the lower part of a room, it produces a draught; if admitted at the top of a room, being heavier, it falls by its own weight on the heads of those in the room. The problem of ventilation is to secure a sufficient interchange of air without the production of perceptible currents.
Movements of air are constantly occurring, so long as the temperature of the air is subject to changes. This cause alone will suffice to ventilate all rooms in which the air is hotter than the external air. It may thus happen that a room with windows and doors closed in winter, may possess purer air than the same room in summer with these thrown widely open. The value of diffusion of air through the walls, and the influence of temperature on this diffusion are well illustrated by some experiments of Pettenkofer.
When the difference between the outside and inside temperatures was 34° Fahr. (66° inside and 32° outside), and the doors and windows were shut, an ordinary room in his house, of the capacity of 2,650 cubic feet, which was built of brick, and furnished with a German stove instead of an open fire-place, had its entire atmosphere changed once in an hour. With the same difference of temperature, but with the addition of a good fire in the stove, the change of air rose to 3,320 cubic feet per hour. On lessening the difference between the external and internal temperature to 7° Fahr. (64° and 71°), the change of air was reduced to only 780 cubic feet per hour. In these experiments, all crevices and openings in doors and windows were pasted up.
It is instructive to note the greater amount of ventilation effected through the walls, etc., than by the draught of the stove.
The amount of ventilation through walls varies with the material of which they are built. Mortar is exceedingly porous when dry; sandstones and bricks are easily permeated by both water and air. Limestone is almost impervious to air, but requires much mortar in building, which effects a partial compensation (see page [206]).
The rise of temperature caused by the bodily heat and by the combustion of illuminating agents, is well shown by some figures of Dr. Angus Smith. He found that the rise of temperature of 170 cubic feet of air in one hour, produced by the bodily heat of one man was 5°·6 Fahr.; by the combustion of a candle 3°·8 Fahr. Thus, in a room 8 feet high, 4 feet broad, and 6 feet long, a man burning a candle would in an hour raise the temperature from 60° to 70° Fahr. This rise in temperature would not only cause currents of hot air towards the upper part of the room, but would probably make the room uncomfortable, and so lead to the opening of a door, etc.
(3) Winds are of great value in flushing rooms with fresh air. They ought to be utilised as often as possible, by throwing windows widely open; without, however, taking the place of constant ventilation in the intervals. They are especially valuable in getting rid of organic matters which are unaffected by diffusion.
The wind will pass through wood, and even brick and stone walls. When it is allowed to pass directly through a room, as from window to door, it produces a more powerful effect than can be produced in any other way. The average rate of movement of winds in this country is 10 feet per second, or about 7 miles an hour. If the surface which a man exposes to this average wind = 6’ × 1½’ = 9 square feet, then 90 cubic feet of air flows over him in one second, and 324,000 in an hour. If 3,000 cubic feet were the allowance for each person indoors—a much greater allowance than is usually given—he only receives 1 ∕ 108 of the air with which he is supplied in the open.
Winds act as a ventilating agent in two ways—directly by perflation, driving impure air before them, or freely mixing with it; and indirectly by aspiration, drawing the impure air along with them. In the last case, the wind causes a partial vacuum on each side of its path, towards which all the air in its vicinity flows. Thus, the wind blowing over the top of a chimney causes a current at right angles to itself up the chimney. In a spray-producing apparatus we have a familiar instance of the same principle, the current of air or steam along the horizontal tube causing the fluid to rise in the vertical tube till it is scattered in spray. In Sylvester’s plan of ventilation, both these forces are used (see page [150]).
4. Certain Constituents of the Atmosphere have an important purifying effect. Of these oxygen is by far the most important. By its means organic impurities become oxidised, and thus rendered harmless. It is probable that much of this oxidation is effected by means of ozone—a peculiarly active and concentrated form of oxygen. A large part of this ozone is probably produced during thunderstorms and similar electrical disturbances of the atmosphere. The ammonia and organic impurities in air become changed into nitrites and nitrates—chiefly of ammonium—and being washed down by rain, form an important part of the food of plants.
5. For Chemical Measures of purification of the atmosphere see page [324].
[CHAPTER XX.]
GENERAL PRINCIPLES OF VENTILATION.
The Amount of Air required.—Ventilation is chiefly concerned with the removal of the products of respiration, just as sewage is chiefly concerned with the removal of the solid and liquid excreta.
In a less degree it is required for removing the impurities produced by the burning of gas, candles, and lamps. The main problem, however, is the removal of the respiratory products.
The amount of carbonic acid in air is usually fairly proportional to that of the other respiratory products. It may therefore be taken as a measure of the impurity of the air. There are, however, certain fallacies in this test. In soda water manufactory, for instance, there would be a comparatively harmless excess of carbonic acid. In dirty rooms, and in hospitals and other institutions where rooms are not vacated for a considerable period, the amount of organic matter present is often in excess of what would have been anticipated, judging by an estimation of the carbonic acid. This is strikingly shown by some valuable researches at Dundee, which are summarised in the following table. If we take the average amount (in excess of outside air) of carbonic acid, organic matter, and micro-organisms respectively in houses of four or more rooms as unity, then in one or two-roomed houses or tenements we have as follows:—
| HOUSES OF FOUR ROOMS AND UPWARDS. | TWO-ROOMED HOUSES. | ONE-ROOMED HOUSES. | |
|---|---|---|---|
| Carbonic acid | 1 | 1·5 | 2·0 |
| Organic matter | 1 | 1·6 | 4·4 |
| Micro-organisms | 1 | 5·1 | 6·7 |
It is evident that in these cases the carbonic acid did not increase in the same proportion as the organic matter and micro-organisms, and that it alone does not form a sufficient test of the impurity of any given atmosphere. The amount of carbonic acid, however, is a valuable and convenient test of the condition of the air of a room, and the problems of ventilation, of which examples are given on page [137], are based on its amount.
The Standard of purity is somewhat difficult to fix. The external air ought only to contain 4 parts of carbonic acid to 10,000 parts; but it is almost impossible to maintain this degree of purity in inhabited rooms. The experiments made by Drs. Parkes and De Chaumont showed that when the carbonic acid is ·06 per cent., or in the proportion of 6 parts in 10,000 of air, the air begins to be perceptibly stuffy (page [125]); this may therefore be taken as the limit of impurity. Pettenkofer has adopted the limit of ·07 per cent.[7]
The problem then is to discover the amount of pure external air (containing ·04 per cent. of carbonic acid) that will be required to pass hourly through a room, for every person in that room, in order to keep the carbonic acid at the ratio of ·06 per cent.
This may be ascertained by actual observation of the air of rooms in which a given number of persons are placed; or by calculations from physiological data.
As the result of numerous experiments on the atmosphere of prisons, barracks, etc., where the amount of fresh air supplied per hour is exactly known, it is found that in order to keep the carbonic acid at ·06 per cent., 3,000 cubic feet of pure air are required per head per hour; 2,000 cubic feet keep the carbonic acid at ·07 per cent.; 1,500 cubic feet at ·08 per cent.; and 1,200 cubic feet at ·09 per cent.
For the removal of the products of combustion of gas, an additional supply of air is required, for the amount of which, see page [116].
Where a number of sick persons are collected, as in hospitals and workhouses, a much freer supply of air is required. Much depends, however, on the cleanliness of the wards, and on whether the ventilation is constant in character. In St. Thomas’s Hospital, the space allotted to each ordinary patient is 1,800 cubic feet, and to each patient in the fever wards 2,500 cubic feet. Thus, by changing the air of the wards twice in the hour, an abundant supply of fresh air is ensured. The mortality after operations, and in all fevers, is much diminished by a free supply of air.
Soldiers are allowed 600 cubic feet of space per head in their sleeping rooms, which involves a change of the air five times per hour, in order that the carbonic acid may be maintained at ·06 per cent. The limit of overcrowding for lodging-houses is usually fixed at 300 to 500 cubic feet, but this is too little.
The amount of pure air required in order to keep the carbonic acid in a room at ·06 per cent., may also be ascertained from physiological data.
An average adult expires 3 ∕ 5 (·6) cubic foot of carbonic acid per hour. Now as the carbonic acid in air to be breathed must not contain more than two parts in 10,000 (·02 per cent.) in excess of what is present in external air (·04 per cent.), it follows that if x = the amount of fresh air required by an adult per hour in order to keep the carbonic acid in the room down to .06 per cent., then:—
·02 : ·6 :: 100 : x.
x = 3,000 cubic feet.
Relation of Air Required to Cubic Space of Room.—If we accept 3,000 cubic feet of air as the amount required per head per hour, this may clearly be furnished by having a large room with comparatively little circulation of air, or by having a small room with frequent interchanges. Thus, supposing the cubic space allowed to each individual is 1,000 cubic feet—that is, 10 feet in every direction—the atmosphere will require changing three times per hour.
Now, it is found that when a current of air, at the temperature of 55°-60° Fahr., is moving at the rate of less than one mile per hour, it is not perceptible—that is, produces no draught. The rate of a breeze, which is just perceptible, is 18 inches per second, or one mile per hour. As draughts are objectionable, ventilation, in the best sense of the word, means the supplying of abundant fresh air at a rate of less than one mile per hour, or warmed air at a higher rate. Air moving at the rate of 2½ miles per hour, or 3½ feet per second, is perceived as a slight draught by all, at the average temperature of our climate (about 50° Fahr.)
Where natural ventilation is employed, the difficulties of thoroughly ventilating a small space, without draught, are very great.
A change of air three or four times in an hour is all that can be borne under ordinary conditions in this country, and this necessitates a supply of 1,000 or 750 cubic feet of space respectively for each individual. And a change of this frequency is commonly not effected; the ventilating apparatus may fail temporarily, or may be wilfully stopped up, or there may be no means of ventilation; it is essential therefore to have as large a cubic space as possible. A large cubic space, does not obviate the necessity for efficient circulation of air. It is, however, advantageous, not only on account of the initial longer time before the air reaches the limit of impurity, but also because there are less draughts, and there is a larger wall surface and larger windows for unperceived ventilation.
Common Errors as to Ventilation.—(1) In relation to the cubic space of a room, it is most important to note that a lofty ceiling does not compensate for deficiencies in floor-space. One hears, “lofty” and “airy” rooms spoken of as though the two terms were necessarily synonymous. This is by no means the case. The impurities produced by respiration tend to accumulate about the persons who have evolved them, although it is true that in rooms heated by gaslight, a large amount of hot and impure air collects near the ceiling. The necessity of an abundant floor-space is shown by the fact that a space enclosed by four high walls and without a roof, will, if crowded, speedily become offensive. Twelve feet is quite high enough for large rooms in schools, hospital wards, etc., and nine feet suffices for the rooms of a private dwelling-house. There is no objection to a greater height, if it is remembered that in reckoning the practical cubic dimensions of a room, the height should only be reckoned as twelve feet. Supposing 500 cubic feet is the amount allowed per individual, then the floor-space should be forty-two square feet, which would be furnished by a room about 8½ feet long and 5½ feet wide. In barracks, soldiers are allowed fifty square feet of floor-space. In school-rooms the Education Code requires that at least ten square feet of floor-space, and at least 120 cubic feet shall be allowed for each child in average attendance.
(2) It is commonly supposed that a large room compensates for a deficient circulation of air. The cubic space of a room is really of less importance than the capacity for frequent interchanges of air. Even the largest enclosed space can only supply air for a limited period, after which the same amount of fresh air must be supplied, whether the space be small or large. Thus, supposing that as large a space as 10,000 cubic feet per head were allowed, the limit of purity would in the absence of ventilation be reached in three hours, and after that time an hourly supply of 3,000 cubic feet of air would be just as necessary as if the space were only 200 cubic feet.
(3) It must not be overlooked that the furniture in a room must be deducted from the breathing space, as the amount of air is diminished by the space occupied by the furniture. About 10 cubic feet ought to be allowed for each bed, and 3 to 5 cubic feet for each individual in a room; projecting surfaces must be allowed for by subtraction, and recesses by addition. The deductions to be made for furniture are not of any great consequence, if there is a free interchange of air; as the cubic space is of less importance than free ventilation.
General Rules respecting Ventilation.—The two great objects in ventilating being to remove all impurities from the air, and to avoid draughts, it is important that—
1. The entering air should be, if possible, of a temperature of 55° to 60° Fahr. Whenever the temperature of a room differs from the external temperature by 10° Fahr., a draught is certain to ensue. It is impossible at all times to ensure the incoming air being of the temperature of 60°, without some artificial means of warming it. In this country it is seldom necessary to cool the incoming air, but this may be managed in artificial systems of ventilation by passing the incoming air over ice, or by using compressed air which becomes cooled on expansion, or by passing the incoming air through subterranean tunnels.
2. The entering air should be pure. When a room is hotter than the passages and kitchens, air from the latter, whatever may be its character, is drawn into the room. Similarly the ground-air under the kitchen-floor or the air from ash-pits may be drawn into the house, when no other means of ventilation are provided; and this is often followed by evil results.
3. No draught or current should be perceptible from the incoming air, except when it is wished to flush the room with air, by opening the windows wide. It is a common complaint that a room is draughty, and, to remedy this, keyholes are stopped up, and mats are placed at the bottom of the door, etc. The draught can often be remedied by increasing the size and number of the openings through which air is admitted, so that the current of air is not concentrated and rapid. When this does not remedy it, the incoming air should be warmed. A feeling of draught is very often due to the radiation to and from a window, and disappears when a curtain or screen is placed between the radiating surface and the occupant of the room.
4. The entry of air should be constant, not intermittent. The occasional opening of a window or door will not compensate for the lack of a constant interchange of air, although it forms a very valuable adjunct, especially in the removal of organic particles which do not follow the law of diffusion.
5. An exit should be provided for impure air, as well as an entrance for pure air. The chimney furnishes this in most living-rooms, and diminishes the necessity for other means of exit.
If the openings in a room for entrance and exit are properly regulated, a rate of 5 feet per second (about 3½ miles per hour) will provide sufficient air without any unpleasant draught in a room. For instance, if the opening measure 1 square foot, then a rate of 5 feet per second will give five cubic feet of air per second, that is, 18,000 cubic feet per hour. But as only 3,000 cubic feet are required, it follows that an opening one-sixth this size, i.e. 24 square inches, is sufficient for each individual. Reckoning the same amount for means of exit, 48 square inches is the size of the ventilating orifices required by each individual.
6. A number of small divided openings are not collectively equal in ventilating power to one large one having the same area. Thus, when a ventilating orifice is divided into four parts, which have the same collective area as the original orifice, it is found that only half as much air passes through these as through the original orifice. In order to obtain as much air, therefore, each opening must be equal in size to half the original opening. This is in accordance with the rule that the friction for air passing through openings is inversely to the diameter of these openings, i.e. inversely to the square-root of the area of the openings.
7. The most important requirements of perfect ventilation may be recapitulated as follows:—
1st. The maximum impurity of air vitiated by respiration should not exceed 6 parts carbonic acid per 10,000 volumes.
2nd. To ensure the maintenance of this standard, 3,000 cubic feet of pure air must be supplied per head per hour.
3rd. In order to supply this amount of pure air, with ordinary means of ventilation, 1,000 cubic feet at least must be allowed per head in buildings always occupied.
[CHAPTER XXI.]
PROBLEMS AS TO VENTILATION.
The following formula enables many problems relating to ventilation to be solved. Let p = the amount of poison (carbonic acid) in every cubic foot of fresh air, viz. ·0004 cubic foot. Let A = the number of cubic feet of fresh air delivered or available, P = the amount of carbonic acid exhaled, and x = the amount of carbonic acid per cubic foot in the room at the end of a given time. Then—
x = p + P ∕ A, whence A = P ∕ (x - p).
If the carbonic acid in the air of a room is ·75 per 1,000 volumes (that in the outer air being ·4 per 1,000 volumes), and there are five persons in the room, how much air is entering the room per hour?
- Here x = ·00075.
- p = ·0004.
- P = ·6 (i.e. number of cubic feet of carbonic acid expired by each person per hour).
- Now x = p + P ∕ A.
- ·00075 = ·0004 + ·6 ∕ A.
Therefore A = about 1,700.
Thus 1,700 cubic feet are required for each individual to keep the air within the given limit, and five times this amount will be required for five persons = 8,500 cubic feet.
A room has been occupied for one hour, at the end of which the total carbonic acid present was found to be 1·1 per 1,000 parts. The carbonic acid in the open air amounting to ·0004 per cubic foot, find the quantity of air supplied per hour.
- Here x = ·0011.
- p = ·0004 and P = ·6.
- Hence ·0011 = ·0004 + ·6 ∕ A.
- Therefore A = 857 cubic feet.
If six persons are in a room containing 3,000 cubic feet, and there is a supply of 2,000 cubic feet of air per head per hour; how much carbonic acid is there in the air of the room at the end of 4 hours?
- Here p = ·0004.
- P = ·6 × 6 × 4 = 14·4.
- A = 2,000 × 6 × 4 + 3,000 = 51,000.
- x = ·004 + 14·4 ∕ 51,000 = ·000682 = 6·82 parts CO₂ in 10,000 of air.
The air of a room occupied by 6 persons and containing 5,000 cubic feet of space, yields 7·5 parts of CO₂ per 10,000 parts of air. How much air is being supplied per hour?
A = P ∕ (x - p) = ·6 x 6/(·00075 - ·0004) = 10,280 cubic feet.
In the same room what would be the condition of the air at the end of 4 hours?
x = ·0001 + ·6 × 6 × 4/(10280 × 4 + 5,000)
= ·0004 + 14·4 ∕ 46,120 = ·000712 = 7·12 of CO₂ in 10,000 of air.
Given two sleeping rooms, Y 10 ft. by 15 ft. and 10 ft. high, Z 15 ft. by 20 ft. and 12 ft. high, with three adults in each; how much fresh air would you supply in each? What would be the condition of the air of each of the rooms after, ¼;, ½, 1, and 2 hours respectively?
Amount of fresh air to be supplied in Y—
A = P ∕ (x - p) = ·6 × 3/(·0005 - ·0004) = 9,000 cubic feet per hour.
Condition of air in Y after ¼ hour—
Here p = ·0004.
P = ·6 × 3 ∕ 4= ·45.
A = 9,000 ∕ 4 + 1,500 = 3,750.
x = ·0004 + ·45 ∕ 3,750 = ·00052.
At the end of 2 hours—
x = ·0004 + 3·6∕(18,000 + 1,500) = ·000584.
And similarly for Z.
Suppose two rooms, one 10 feet cube, the other 50 feet by 20 feet and 15 feet high, have continuously admitted into each of them a volume of fresh air containing ·04 parts carbonic acid per 100 parts, amounting to 2,000 cubic feet per hour, so as to replace to that extent the air of the room; suppose also that an average adult be placed in each room: show by detailed calculation what would be the condition of impurity of air in each room, as measured by carbonic acid, at the end of 4 hours and 12 hours respectively.
In the case of the first room—
- P = ·6 × 4 = 2·4.
- A = 2,000 × 4 + 1,000 = 9,000.
- p = ·0004.
- x = ·0004 + 2·4 ∕ 9,000 = ·000667.
The amount of impurity at the end of 12 hours, and in the second room may be similarly ascertained.
Ventilation in relation to Temperature.—The temperature of a given atmosphere is a most important factor in determining the ease with which it is replenished from the external air. Speaking generally, the greater the difference between the temperature of two masses of air the more rapidly an interchange occurs.
Air has weight. A column of it one inch square and extending to the uppermost limit of the atmosphere weighs about 14·6 lbs., and exerts this pressure on all substances at the surface of the earth. This pressure is exerted uniformly in all directions; but for this fact our chests would be crushed in by the external pressure on them, which amounts to over four tons. If the atmospheric pressure is diminished at any point, it is evident that the surrounding air will tend to press in this direction. Now, when air is heated it expands, and consequently the heavier fresh air flows in from all sides and pushes the lighter air upwards.
The expansion of air for every increase of 1° Cent. is ·003665 (1 ∕ 273), for every increase of 1° Fahr. is ·00203 (1 ∕ 492). Thus if the air in a room is 20° F. warmer than that outside, it will be expanded to 1 ∕ 25 additional bulk.
Thus if M = volume of a given air at 32°, with the barometer at 30 inches, and
M1 = volume at temperature t° above 32°, while a = co-efficient of expansion for each degree of elevation of temperature, then the dilatation effected by heat will be expressed by the formula—
M1 = M (1 + at).
When the temperature is decreasing
M1 = M (1-at).
If the air in a chimney flue is cooler than the air of the room with which it communicates, it will flow down into the room. It is the object of an economical fire-place to cause the chimney to act as an outlet for the products of combustion and for the impurities of the air of the room with the smallest possible waste of heat. Short of producing a down draught of cold air and smoke, the smaller the difference between the temperature of the air of a room and of the air escaping near the top of the chimney, the greater the economy of fuel.
The movement of air in flues and other outlets is governed by general laws, like those governing the general movements of fluids, but allowances require to be made for friction in the channels of entrance and outlet.
The theoretical velocity, when friction is not taken into account, may be calculated by a formula based on what is known as the law of Montgolfier, or the law of spouting fluids. According to this law, fluids pass through an opening in a partition with the same velocity as a body would attain in falling through a height equal to the difference in depth of the fluid on the two sides of the partition, i.e. to the difference of pressure on the two sides. Thus, if AB equals the height of a column of air at, say, 50° F., and AC is the height of the same quantity of air heated to 60°, then the velocity with which the warmer air ascends will be that which a body would acquire in falling from C to B.
Now the velocity in feet per second of falling bodies is about eight times the square root of the height from which they have fallen; and the formula for determining this is—
v = c √(2gh) = 8·2c √h.
- g = 32·17 feet per second;
- h = distance fallen through by the body;
- c = a constant determined by experiment, and expressing the proportion of the actual to the theoretical velocity.
Adapting this formula to the special circumstances under which Montgolfier’s formula holds, we find that the force which drives the warm air up the flue is the force of gravity, i.e. of the excess of the weight of a column of cold air over the weight of a column of warm air of exactly the same size (represented by BC in the preceding diagram). The difference of the two weights or pressures is found by multiplying the distance from the point of escape of heated air out of the room (fire-place or elsewhere) to the point of escape into the outer air (top of chimney or other point of exit), by the difference in temperature inside and outside, and again multiplying this product by 1 ∕ 492 for degrees of Fahrenheit temperature, or 1 ∕ 273 for degrees Centigrade.
Thus omitting c for the present, we have—
v = √(2gh(t - t1)/492) = 8·2√(h(t - t1)/492)
Where t = temperature in the chimney,
t1 = temperature of the external air, and
h = height of chimney.
Example.—The chief means of ventilating a given room is by its open fire-place. The temperature in the chimney is 100° F., that of the external air 40°, and the height of the chimney 50 feet; what is the velocity with which air is leaving the room?
v = 8·2 √((100 - 40) × 50 ∕ 492)
= 20.
This gives the theoretical velocity, but the real velocity will differ from the theoretical by an amount varying from 20 to 50 per cent.
It will be evident, from what has been said, that the movements of the air in a confined space are dependent upon (1) the difference between the internal and external temperatures; (2) the area and friction at the apertures through which air enters and leaves the room; and (3) the height of the column of ascending warm air. The higher the chimney (assuming it to contain warm air), the greater the draught and the more efficient the ventilation of the room communicating with it. Hence ventilation is more difficult in upper rooms of large houses and in single-storeyed houses than in the lower storeys of large houses.
Allowance for Friction.—Practically the friction varies greatly according to the size, form, and material of outlet for air. A rough or sooty or angular chimney greatly impedes the outgoing current of air.
It is usual to reduce the theoretical velocity by 20 to 50 per cent. Apart from the friction which is governed by roughness and length of channels, that due to bends in the channel may be calculated by the formula 1/(1-sin2 θ), θ being the angle at any bend in this channel.
(It may be convenient to note that—
- sin2 90° = 1,
- sin2 60° = ¾
- sin2 45° = ½,
- sin2 30° = ¼.)
Thus every right angle in a bent shaft reduces the velocity in it by one-half.
The loss by friction in two similar tubes of equal sectional area varies (1) directly with the square of the velocity of the air currents; and (2) directly with the length of the outlet channel. In two similar tubes of unequal size the loss by friction is (3) inversely as the diameter of the cross-section in each.
When two tubes are of different shapes, the loss by friction is inversely as the square roots of the sectional areas.
Owing to the variable value of the co-efficient of friction (called c in the first formula given), it is usually preferable to measure the actual rate of progress of air through a given flue by means of an anemometer (wind measure). Then the velocity of the current of air and the area of the cross section of the flue being given, the volume of air discharged in a given time is represented by the product of these two and the time which has elapsed.
Thus, q = a × v.
Where q = quantity of air discharged in a given time, a = area of cross section of flue, v = velocity of current.
By means of this formula, the area of chimney required to discharge a given volume of air at a given average velocity can be ascertained. Thus—
a = q ∕ v.
The application of the preceding principles and formulæ will be rendered clearer by the following examples.
How much inlet and outlet area per head will be required to give 10 persons in a room of 5,000 cubic feet capacity, 2,000 cubic feet of air per head per hour, supposing that the outside temperature is 40°, while the internal temperature is 60°, and the height of the heated column of air 20 feet?
First ascertain the velocity of entrance and exit of air.
v = 8·2√(h(t - t1)/492)
= 8·2√(20(60 - 40)/492) = 8·2 × ·902.
= 7·3964 = velocity in feet per second.
If we allow one-fourth for friction, then there remains a velocity of 5·5473 feet per second.
5·5473 feet per second = 19700·8 feet per hour.
Now, a = q ∕ v
= 2,000 ∕ 19700·8 = ·1015 square feet.
= 14·6 square inches.
Thus the size of the outlet required per head is 14·6 square inches. The size of the room and the number occupying it do not enter into the question, except for a short time at the beginning. (See page [135].)
The amount of inlet required will also be 14·6 square inches per head. Theoretically it ought to be slightly less than that required for outlet, as the outgoing air is more expanded than that entering the room; but practically no allowance need be made for this fact.
The total amount of inlet and outlet required per head = 29·2 square inches.
If the mean temperature of a room is 61°, the external temperature 45°, while the heated column of air is 50 feet, and the required delivery of air 2,000 cubic feet per hour, find the size of inlet and outlet.
v = 8·2√(h(t - t1) ∕ 492)
= 8·2√(50(61 - 45) ∕ 492)
= 10·55 feet per second.
= 37,980 feet per hour.
If we make no allowance for friction, then
a = q ∕ v
= 2,000 ∕ 37,980 square feet.
= 2,000 × 144 ∕ 37,980 = 7·58 square inches.
This gives the required size of outlet. The size of inlet and outlet together = 15·16 square inches.
If 3,000 cubic feet of air are supplied in one hour through an aperture of 12 square inches to a room containing 1,000 cubic feet of space, at what rate does the air enter the room?
12 square inches = 1 ∕ 12 square foot.
a = q ∕ v
1 ∕ 12 = 3,000 ∕ v
Therefore
v = 36,000 feet per hour.
= 10 feet per second.
If a room is supplied with 3,000 cubic feet of air per hour, through a single opening, what must be its area, if the rate of movement of the air is 5 feet per second?
5 feet per second = 18,000 feet per hour.
a = 3000 ∕ 18000 = 1 ∕ 6 square foot.
= 24 square inches.
As already stated, the difficulties connected with the estimation of amount of friction greatly detract from the practical value of the formulæ just given. Even the results given by anemometers are not always trustworthy, but by comparing the results given by them with those obtained by the use of Montgolfier’s formula an approximation to the truth can be obtained.
The ordinary anemometer consists of four tiny vanes fixed to a spindle, so that revolutions are caused by the current of air the velocity of which is to be measured. The revolutions are counted by a mechanical arrangement. The value of the revolutions of the vanes has to be first determined by direct experiment; a known bulk of air being forced through a channel of known size at a uniform rate, and the instrument graduated accordingly. In Fletcher’s anemometer a modification of the manometer or pressure-gauge has been used for the same purpose.
Inlets and Outlets.—Having given the average velocity of the wind, the size of a room, and the number of persons occupying it, the size of inlet opening required can easily be calculated.
Find the size of inlet for air in a room occupied by one person, the air moving at the average velocity of 5 feet per second, assuming that 3,000 cubic feet of air are to be supplied per hour.
Let x = size of inlet.
Then x × 60 × 60 × 5 = 3,000.
Therefore x = 3000 ∕ 18000 = 1 ∕ 6 square foot.
= 24 square inches.
Given that the air moves at a velocity of 10 feet per second, and that the area of the inlet aperture into a room is 12 square inches, find how much air enters the room in an hour.
Let y = amount of air.
Then 10 × 60 × 60 × 12 ∕ 144 = y.
Therefore y = 3,000 cubic feet of air.
Calculations as to supply of air in a room founded on the average velocity of air-currents are, however, much less trustworthy than when the velocity is determined, as previously explained, by means of Montgolfier’s formula, or, better still, by an anemometer.
The Commissioners on Improving the Sanitary Condition of Barracks and Hospitals, in their report (1861) recommended for inlets, one square inch for every 60 cubic feet in the contents of the room; or one square inch for every 120 cubic feet in the contents, if warm air is admitted round the fire-grate. For outlet shafts on lower floors, one square inch to every 60 cubic feet, slightly increasing for the higher storeys.
Amount of Air-space required.—We may take 3,000 cubic feet of air as the average amount of air required hourly by each individual, and inasmuch as the air of a room cannot be changed oftener than three times an hour without producing an unpleasant draught, it follows that at least 1,000 cubic feet of space must be allowed per person.
This may be compared with the amount actually supplied under various circumstances.
| In the British Army for each soldier— | |||
| In permanent barracks | 600 | cubic ft. | |
| In wooden huts | 400 | „ | |
| In hospital wards at home | 1,200 | „ | |
| In hospital wards in the tropics | 1,500 | „ | |
| In general hospitals | 1,000-1,500 | „ | |
| In fever hospitals | 2,000-3,000 | „ | |
| In workhouse hospitals | 850-1,200 | „ | |
| In common lodging houses | 300 or 350 | „ | |
| Do., if occupied night and day | 350 or 400 | „ | |
| In workhouses | 300 | „ | |
| In schools— | |||
| London School Board requires per scholar | 130 | „ | |
| English Educational Code per scholar (minimum), in old schools | 80 | „ | |
| Do., in new schools | 120 | „ | |
Floor-space has an important bearing on ventilation. In calculating the available cubic space of a room, the height over 12 feet should be disregarded. Thus, if 500 cubic feet is allowed for each individual, the floor-space should be 42 square feet. In barracks, soldiers are allowed 50 square feet of floor-space.
In the Government regulations for workhouses it is stated that there must not be more than two rows of beds, and that the height of rooms above 12 feet must not be reckoned. This gives a minimum floor-space of 25 square feet per occupant, or with dormitories 17 feet wide, a bed-space of about 3 feet.
In hospitals, the question of floor-space is extremely important, as it regulates the distance between the sick inmates and the convenience of nursing. Assuming each bed to be 3 feet wide and 6½ feet long, the distance between any two beds should be at least 5 feet. This makes the wall-space for each bed 8 feet long, and allows from 80 to 96 square feet of floor-space per bed. At St. Thomas’s Hospital, London, the floor-space is 112 square feet, and in fever hospitals it is from 150 to 300 square feet per bed. In regard to the ventilation of hospitals, it has been well said that nothing less than too much is enough.
Means of ascertaining Cubic Space.—Circumference of a circle = Diameter (D) × 3.1416.
- Area of circle = D2 × .7854.
- Area of square = square of one of its sides.
- Area of rectangle = product of two adjacent sides.
- Area of triangle = base × ½ height, or height × ½ base.
- Area of ellipse = product of the two diameters × ·7854.
- Circumference of ellipse = half the sum of the two diameters × 3·1416.
- Area of any polygon found by dividing into triangles, and taking the sum of their areas.
- Cubic capacity of a cube found by multiplying the three dimensions together.
- Cubic capacity of a cylinder = area of base × height.
- Cubic capacity of a cone or pyramid = area of base × 1 ∕ 3 height.
- Cubic capacity of a dome = area of base (circle) x 2 ∕ 3 height.
- Cubic capacity of a sphere = D3 x ·5236.
- Area of segment of a circle found by adding to ⅔ of product of chord and height, the cube of the height divided by twice the chord.
(Ch x H x ⅔) + H3 ∕ (2 Ch)
Give the dimensions of a circular ward for 12 patients, each to have 1,750 cubic feet of available air-space.
Capacity of ward = 1,750 X 12 = 21,000 cubic feet.
If we allow 120 square feet floor-space for each patient, then the total floor-space will be 1,440 square feet. Consequently the height of the ward = 21000 ∕ 1440 = 14·75 feet.
- Area of circle = D2 x ·7854.
- 1,440 ∕ ·7854 = D2.
- Therefore D = 43·2 feet.
- Circumference of circle = D x 3·1416.
- = 43·2 x 3·1416.
- = 135·7 feet.
The dimensions of the circular ward required are therefore a height of 14·75 feet, diameter of 43·2 feet, and circumference of 135·7 feet.
Find the cubic capacity of a circular hospital ward 28 feet in diameter, 10 feet high, and with a dome-shaped roof 5 feet high.
- Area of floor-space = D2 x ·7854.
- = 614·8 square feet.
- Cubic capacity of the cylinder below the dome is 614·8 x 10 = 6,148 cubic feet.
- Cubic capacity of dome = 614·8 x ⅔ x 5 = 2049·3 cubic feet.
- Total cubic capacity of the ward = 8197·3 cubic feet.
In practical measurements of rooms, deductions must be made from the cubic space for the furniture contained in it and for its inmates. About 10 cubic feet ought to be allowed for each bed and bedding, and 2½ to 4 cubic feet for each individual. Projecting surfaces must be allowed for by subtraction, and recesses by addition.
A circular ward with a diameter of 36 feet has a dome-shaped roof, the height of whose centre is 18 feet. The height to the dome is 12 feet. Find the floor-space and total cubic contents. How many patients ought the ward to accommodate?
- Area of floor-space = (36)2 x ·7854.
- = 1017·8784 square feet.
- Cubic capacity of cylinder below dome = 1017·87 x 12 = 12214·5 cubic feet.
- Cubic capacity of dome = 1017·87 x ⅔ x 6 = 4071·48 cubic feet.
- Total cubic capacity of the ward = 16285·98 cubic feet.
Assuming that 1,500 cubic feet are required for each patient, then the ward is large enough for 10 patients. It is well to test this conclusion by calculating whether sufficient floor-space has been allowed for each patient. The floor-space has been found to be about 1,018 square feet, which would give 100 feet for each of 10 patients and more than the minimum standard previously stated.
What number of people should be allowed to sleep in a dormitory 40 feet long, of which the accompanying sketch is a section?
The cubic capacity of the quadrilateral space below the roof = 16 x 9 x 40 = 5,760 cubic feet.
Area of floor = area of base of roof = 40 x 10 = 640 square feet.
- Cubic capacity of roof = 640 x ⅓(13 - 9).
- = 853·3 cubic feet.
- Total cubic capacity of dormitory = 6613·3 cubic feet.
If we take the low standard of common lodging houses and allow 350 cubic feet of space for each inmate, then 18 persons may be allowed to sleep in the dormitory.
How much space would a man occupy supposing him to weigh 175 lbs.? How much is usually allowed for a man with his clothes, bed and bedding?
The space occupied by a man is stated by Parkes to be from 2½ to 4 cubic feet (say 3 for the average). He gives the following rule: The weight of a man in stones divided by 4 gives the cubic feet he occupies. Thus, a man weighing 175 lbs. would occupy 3⅛ cubic feet of space.
About 10 additional cubic feet must be allowed for clothing, bedding, and bed for each person.
What size of inlet and outlet aperture should be allowed per head? How large should each individual inlet be made? If an inlet aperture 100 square inches in area is divided into four, with apertures of 25 square inches each, what is the loss by friction?
A size of 24 square inches per head for inlet and the same for outlet meets common conditions.
It is desirable to make each individual inlet not larger than 48 to 60 square inches in area, i.e. large enough for two or three men; and each outlet not larger than one square foot, or enough for six men (Parkes). This ensures more uniform diffusion of the air throughout a room. On the other hand, the loss by friction is greatly increased by having a number of small openings instead of one large opening. This loss is inversely to the square roots of the respective areas. Thus the square root of 100 is 10; the sum of the square roots of the four apertures of 25 square inches each is 20. The loss by friction is double in the second case what it was in the undivided opening. It is evident, therefore, that in order to get as much air through the four openings as through the original large opening, each must be equal in size to half the original opening.
Why is ventilation more difficult in upper rooms of large houses and in single-storied houses than in the lower storeys of large houses?
Cold external air being heavier than the internal warm air presses downwards to the lowest point, and pushes up the warmer air. If there were a vacuum in the room, air would rush into it with a velocity which, as seen before, is represented by the formula—
v = √(gs).
Where g = 32, s = height of column of air, which we may take as roughly 5 miles.
From this formula we obtain v = 1,306 feet per second.
It is evident that in such a case the velocity of entry of air into a vacuum on the ground floor would be greater than into a vacuum on any of the higher storeys, owing to the greater velocity acquired through the increased action of gravity.
And the same increased facility of entry of air into lower rooms must hold good under ordinary circumstances, inasmuch as by Montgolfier’s formula (which is founded on the fundamental formula v = √2(gs))
v = √2(gh(t-t1) ∕ 492)
h = distance between top of chimney and floor of room in question, and thus the velocity with which air enters is governed by the difference between the internal and external temperature, and the height from which the cold air descends in order to take the place of the air which has escaped.
[CHAPTER XXII.]
METHODS OF VENTILATION.
In most houses no special means of ventilation are provided, windows, doors and fire-places being trusted for ensuring a sufficient supply of fresh air. These do not suffice in well-built houses, unless the inhabitants train themselves into enduring the currents of air necessarily associated with open windows and doors. They are, however, aided in the majority of houses by the porosity of walls, by currents of air through crevices of wood-work, and so on. It is desirable that adequate special provision for ventilation should be made for every house when it is built, and that as much care and forethought should be exercised in this respect as in the laying on of a water-supply or sanitary appliances connected with drainage.
Whatever the system of ventilation adopted, it is wise to flush rooms frequently with fresh air. This is best effected by throwing the windows wide open whenever a room is left unoccupied. In this way a much more thorough and complete purification is effected than by any other means. This is especially important in the case of bedrooms, in which organic impurities are most prone to accumulate.
Not only should rooms be ventilated, but likewise the furniture they contain. This again is most important for bedrooms. Beds should not be “made” till sometime after using; and in the interval, should be freely exposed to the air. The same applies to night apparel.
It is well to allow rooms to lie fallow at intervals. Organic matter accumulates about a room, and devitalises any air which enters. If the room is vacated, and flushed with air for a continuous period, it becomes sweeter and purer. The importance of this is now well recognised in the case of hospital wards. Such temporary disuse of rooms must not, however, be regarded as sufficient without thorough cleansing of every surface in them, in order effectively to remove all organic and other dust.
An Inlet and Outlet for air should both be provided. According to some an inlet only is required, while others would only provide an outlet; but a perfect system of ventilation requires both. As heated air expands, the outlets should theoretically be larger than the inlets; but as the average difference of temperature is only 10°-15° Fahr., the expansion is only slight, and may be practically neglected.
The necessity for both inlets and outlets may be illustrated by a single apparatus like that shown in Fig. 11. A taper is burning at the bottom of the jar, in the stopper of which two tubes, A and B, are placed. So long as both tubes are kept open the candle will keep alight, but if A be blocked, the candle goes out.
Fig. 11.
Illustrating Necessity of Inlet and Outlet.
Inlets should bring air from a pure source, and should be arranged at intervals in large rooms. Externally, inlets should be protected from the wind; and the shorter the inlet tubes the better, as thus a current is ensured, and they can be easily cleaned. The position of inlets should not be too near the outlets, otherwise the fresh air may escape immediately. The best position for inlets is at the floor, but this necessitates warming the entering air, as otherwise it would be intolerable, except in summer time. If the air cannot be warmed, it should he admitted about seven feet above the floor, and directed upwards. For size of inlets, see page 142.
Outlets, under ordinary circumstances, are best placed near the ceiling. They should be enclosed as far as possible within walls, so as to prevent the outgoing air being cooled; and should have smooth walls, reducing friction to a minimum. Where artificial warmth increases the temperature of the air, the discharge of outlets is much more certain and constant. The chimney with an open fire forms one of the best outlets. Gas, again, may be made to heat an outlet tube, which carries off the products of combustion.
Two forms of ventilation are usually described—natural and artificial. The former term is used to describe any plan not requiring heating apparatus or the motive power of steam, or gas, or electricity, while the latter implies the use of some such motive power or source of heat. Obviously, however, there is no sharp line of demarcation between the two. A lighted fire is strictly an artificial plan of ventilation, but inasmuch as no apparatus intended for ventilating purposes is required, it is hardly a means of artificial ventilation.
Natural Ventilation.—The most important means of natural ventilation are the window and the chimney; but openings in outer walls and over the door may form valuable adjuncts.
The Window is perhaps the most important agent in purifying a room—both the light and air it admits being essential for health. The window is invaluable (1) for flushing the room with fresh air at intervals. Where possible, opposite windows should be opened, or window and door. Cross-ventilation by opposite windows open at the top forms one of the best means of natural ventilation, in large rooms, such as school-rooms. This can, as a rule, be borne without discomfort, while the room is occupied, unless the wind is very high.
(2) The Upper Segment of a window may be made to work inwards on a hinge, and turned so that the current of air may be upwards. Where this plan is adopted, triangular pieces of glass should be placed at the two sides to prevent cold air from falling directly down at the sides of the opening.
(3) A Block of Wood, two or three inches wide, may be inserted at the bottom of the window sash at A (Fig. 12), and then the window pulled down on this. The consequence is that air is admitted between the two sashes at B, its current being necessarily directed upwards (Fig. 12). This plan answers admirably in admitting pure air; but it possesses a disadvantage common to all the plans in which external air much colder than the internal is admitted into a room. The current of cold air passes upwards for some distance, but may then fall down on the heads of those occupying the room.
Fig. 12.
Window Ventilation.
(4) The top sash of the window may be opened, and some zinc gauze fastened across the open part. This is practically the same as the last arrangement, except that the air is admitted through the apertures of the zinc, and the amount admitted is greatly diminished (page [136]).
(5) In Louvre Ventilators, a number of parallel pieces of glass, each directed upwards, are substituted for a pane of glass. They may be fixed or made movable, as in Moore’s ventilator. The incoming current of air may be similarly directed upwards, in an open window, by arranging Venetian blinds with the laths inclined upwards.
(6) In windows that will not open, Cooper’s Ventilators are often used. Each of these consists of a circular disc of glass, having five oval apertures in it, which works on a pivot through its centre, close in front of one of the panes of a window, which has five similar holes pierced in it. Consequently, when the disc is turned, so that its holes are opposite those of the window, fresh air is admitted. The amount thus admitted is necessarily small.
The Chimney forms the best means of escape of foul air. No room ought to be built without a fire-place, which should never subsequently be boarded up. In bedrooms the chimney forms a most important means of ventilation. If there is no fire, the chimney occasionally furnishes an undesirable source of air; but as a rule the current is upwards, owing to the aspirating action of winds at the top of the chimney. The downfall of air from a chimney chiefly occurs when there is an insufficient inlet for pure air. This is the explanation of smoky chimneys in nine cases out of ten; then the cure is easy by laying on a pipe from the outside of the house to the hearth. When the smoky chimney is due to the contiguity of higher buildings, the chimney must be raised, or a cowl placed over it.
(1) The action of the chimney in carrying impure air away from the room may be considerably increased by narrowing the two ends, so as to produce a more rapid current at the entrance and exit of air.
(2) The heat of the chimney may be utilised by having a separate smaller flue alongside it, with openings from the rooms on each floor. The air in this being heated aspirates the air from each room in succession.
Openings may be made into the chimney-flue at a higher point than the fire-place. These are very valuable for carrying off the heated and impure air resulting from the combustion of gas, as well as for carrying off the respiratory products, which, in their warmed condition, tend to rise towards the ceiling.
(3) Dr. Neil Arnott first devised a valve for this purpose. An opening being made through the upper part of the wall into the chimney, an iron box was inserted, in which was placed a light metal valve capable of swinging towards the chimney flue, but not towards the room. The objections to this apparatus are that it is apt to make irregular clicking noises, and to admit blacks from the chimney when out of order.
(3) In Boyle’s Valve these objections are partially obviated. It consists of an iron frame, across which lie iron rods; and from these are suspended thin talc plates, only capable of moving in the direction of the chimney (Fig. 13). Even this apparatus is rather noisy when there is a strong wind.
View from room.View from chimney.
Fig. 13.
Boyle’s Mica Flap Ventilator.
Neither of these plans answers so well as a second flue alongside the chimney flue, communicating with each room near its ceiling; but the latter can only be arranged for when the house is built, while the valves may be inserted at any time.
The Ceiling may be utilised for removing foul air; and thus serve to diminish the draught which is often produced by the currents of air towards the chimney, when this forms the only means of outlet.
In large rooms (1) a sunlight gas-burner forms an important means of ventilation. It causes a strong up-current from every part of the room. If there is a fire in the room, the burner is apt to become an inlet for air, or the chimney to smoke, according to the relative strength of the two currents.
(2) Benham’s and other forms of Ventilating Gas Burners serve the same purpose. In each of them the products of combustion are conveyed by special ducts above the ceiling to the outer air.
(3) McKinnell’s Ventilator is useful in single-storied buildings, like certain barracks. It consists of two tubes encircling one another, the inner forming an outlet tube, because the casing of the outer tube maintains the temperature of the air in it. It is made higher than the outer tube, and is protected by a hood. The outer tube forms the inlet for fresh air. The entering air is thrown up towards the ceiling and then to the walls by a flange placed at the bottom of the inner tube. The air after traversing the room, and becoming heated, passes upwards to the inner tube. When doors and windows are open, both tubes become outlets; if there is a fire in the room, they may both become inlets; but this may be prevented by closing the outlet tube.
Fig. 14.
McKinnell’s Roof Ventilator.
(4) Various other means have been devised for carrying foul air from the ceiling through channels between the ceiling and the floor of the room above. All share the disadvantage that the channels become dirty and are difficult or impossible of access for cleaning.
(5) Various cowls connected by metal tubes with the ceilings of rooms have been placed on roofs, and their aspirating effect used in ventilating these rooms. When a room is furnished with a chimney such cowls are most undesirable. In large rooms without a fire-place they are helpful, but much more confidence can be placed in cross-ventilation by hinged windows. It is doubtful if any of the advertised fixed cowls produce materially greater aspiration of air from rooms than a simple open tube of the same size. It is desirable that the tube should be protected at its upper end against the entry of rain, and that a grating should be provided to prevent birds building their nests in the tube.
In the preceding plans of ventilation, the ceiling serves almost entirely as an outlet for impure air. In the following plan, it is used as an inlet for pure air.
(6) In Sylvester’s Method of Ventilation, the perflating force of the wind is employed to produce an abundant entry of fresh air. A cowl is placed, always turning towards the wind; the air received is conducted to the basement, where it is warmed by a stove or hot-water pipes, and then passed through tubes into the upper rooms. From these it is carried by tubes above the roof, these tubes being covered with cowls turning from the wind, so that in this way the aspirating power of the wind is likewise used.
Ships are often ventilated in a somewhat similar manner. The tube to which a windward cowl is attached above, ought to be bent at right angles, so as to lessen the velocity of the entering air. By covering other air-shafts with movable cowls, turning from the wind, the aspirating action of the wind is brought into action to aid the escape of foul air.
The Walls of a room, unless covered with an impervious material, are constantly traversed by gentle currents of air, which play an important part in the ventilation of rooms. Special apertures may be made to furnish a freer supply, and these may be in various forms.
(1) A Simple Grating, may be inserted; but this is apt to become blocked with dirt, and does not allow a large amount of air to enter. Louvred openings in the walls are objectionable, except for very large rooms.
(2) Sheringham’s Valve is the most convenient means of ventilating through the wall. An opening in the external wall is made by a ventilating brick or grating; into the wall is fixed an iron box, which has in front of it an iron valve hinged along its lower edge, so that it can open towards the room. On the sides of the valve cheeks are attached, which fit into the box when the valve is shut. A heavy piece of iron pressing against the valve from within the box, tends to keep it constantly open. By means of a string and pulley, the valve can be opened or closed at will, or fixed in any intermediate position.
Fig 15.
Sheringham’s Ventilator
In a very large room, it is better to have several medium-sized valves, than a few larger ones, the air being thus more completely diffused. If there are two valves, they should not be opposite one another, as the air may then simply pass from one to the other, without becoming diffused through the room. If there is only one valve, it may occasionally serve as an outlet when the wind is to leeward. By means of this form of valve, the air is projected upwards in a diverging current towards the ceiling. The valve should be placed above the level of one’s head, but not too near the ceiling; as in the latter case, the current of air is driven hard against the ceiling, and falls thence with considerable force towards the floor. A combination of Sheringham’s inlet and Boyle’s mica outlet into the chimney at the opposite side of the room ensures efficient ventilation in a dining-room. Better than the outlet into the chimney is an opening into a special flue alongside the chimney-flue, if this be available.
(4) Ellison’s Inlet consists of a brick pierced with conical holes, the apex of the cone being towards the external air. By this means any great draught is avoided, and the air is distributed over a considerable area. In order that this may prove an efficient means of ventilation, a considerable number of bricks are required.
The Floor of a room is always the source of considerable currents of air, even when well carpeted. Air mounts up through the crevices of the wood-work, being aspirated into the room when its temperature is higher than that of the rooms below. In the case of rooms on the ground floor, air is often drawn from the subjacent soil, or through dust-bins, etc.
Theoretically, in all measures of ventilation, the floor would be the best point for the entry of cold air. This, however, is intolerable when the incoming air is cold, and the floor must therefore be abandoned as a means of ventilation, apart from heating apparatus.
The floor may be used as a means of entry of fresh air in a modified manner, by directing the air entering at the floor-level for some distance up a tube at the side of the wall. This apparatus is known as Tobin’s tube. It consists of a rectangular or cylindrical tube from 4 to 6 feet high, which communicates at the lowest point with the external air by means of a perforated brick or grating. The air enters the room in an upward direction, and is consequently sent towards the ceiling, where it becomes mixed with warmer air, before diffusing itself throughout the room. But when the incoming air is very cold, it may fall more rapidly, causing cold draughts on the heads of those in the room.
As the air enters directly from outside the house, it often carries with it particles of dirt, soot, etc. This may be remedied by placing a pan containing a shallow layer of water at the lowest part of the tube, or by placing cotton wool at the point of entry of the tube into the room. The tray of water soon dries up and is rarely replaced, while the cotton wool diminishes the amount of entering air. It is very useful however in cold weather, or when fogs occur. A gauze funnel is sometimes inserted in the tube, or a sheet of gauze arranged diagonally across the tube from its highest to its lowest point. The gauze does not keep out minuter particles of dust, and requires occasional cleaning. All Tobin’s tubes, like other ventilating openings, should be made to open, so that their interior can be frequently cleaned.
Summary as to Domestic Ventilation.—Open windows, doors, and fire-places may be in most instances trusted. If gas is used as an illuminant, they should be combined with special arrangements for carrying off the products of combustion from the room. For delicate people, and especially in small rooms, outlet ventilation into the chimney breast combined with a Sheringham’s valve on the opposite wall is desirable.
Artificial Ventilation.—Artificial ventilation may include two important and very different measures. In one of them currents of air and an exchange of pure for impure air are effected by means of various forms of heating apparatus. In the other mechanical measures are used for the same purpose,—the air being either driven out of the room or drawn out of it. In this chapter we shall consider only the mechanical means of artificial ventilation. There are two kinds, the first being known as ventilation by aspiration, or the vacuum system; and the second as ventilation by propulsion, or the plenum system.
In Ventilation by Aspiration the foul air is drawn out of the room by machinery, its place being supplied by fresh air, which may be warmed before entry or not. This plan and the next have been employed chiefly in connection with large buildings, such as hospitals, etc., and in mines.
The extraction of foul air may be effected by—(1) a steam-jet, which is allowed to pass into a chimney, and sets in motion a body of air more than 200 times its own bulk. Tubes from each room of the building are connected with this chimney, and the strong upward current extracts the air from them. This plan is useful in factories, where there is a superfluous supply of steam.
(2) A fan or screw may also be used. The vanes of the fan, when set in motion by electrical or some other motive power, produce a powerful current of air, which can be regulated according to requirements. As in the last plan, the aspirating influence of the fan may be exerted over a system of rooms, by means of connecting tubes.
In Ventilation by Propulsion a fan is used as in the last plan, the air being propelled along conduits leading from it into the room to be ventilated. The size of the conduits being known, the amount of air to be discharged can be regulated by timing the rapidity of the revolutions of the fan.
This plan is suitable for crowded places, where a large amount of air is required in a short time. It is excellent for large schools, churches, and theatres. Its superiority for large elementary schools has been proved at Dundee by the experiments of Drs. Carnelley, Haldane, and Anderson, the results of which are summarised in the following table:—
| NO. OF SCHOOLS. | NO. OF ROOMS. | CUBIC FT. ALLOWED PER PERSON. | CARBONIC ACID IN 10,000 OF AIR. | MICRO-ORGANISMS PER LITRE | ||
|---|---|---|---|---|---|---|
| BACTERIA. | MOULDS. | |||||
| Mechanical ventilation by warmed air | 6 | 32 | 160 | 12·3 | 17·5 | 1·0 |
| Natural ventilation andhot pipes | 17 | 43 | 176 | 16·3 | 96·5 | 1·1 |
| Natural ventilation and open fires | 33 | 84 | 145 | 19·2 | 153·2 | 4·8 |
The air to be admitted may be warmed by passing it over hot-water or steam-pipes. In large establishments, as in hospitals, theatres, etc., it has been arranged so that the incoming air is passed through a screen of coarse cloth, which is kept wet by water trickling down each cord. The air is thus kept moist and freed from dust.
The great advantage of the plan of propulsion, is its certainty. By it the temperature, moisture, and freedom from suspended matters of the incoming air can be exactly regulated and controlled. Its chief disadvantages are that (1) it is somewhat costly, and (2) the apparatus requires skilled supervision. On the other hand it maintains the air in crowded rooms in a condition which cannot be secured by any other method. When combined, as is done in the Houses of Parliament, with the use of a flue for the extraction of foul air, this plan answers admirably.
The Relative Value of Artificial and Natural Ventilation scarcely needs to be discussed. They are both valuable, but under different circumstances. In dwelling-rooms natural ventilation by doors, windows and chimney usually suffices, especially if the products of combustion of gas are removed through a special flue. Natural ventilation is always occurring, and only needs a little aid in domestic life. For large rooms occupied by many persons artificial ventilation is necessary to maintain pure air.
Whatever method of ventilation is adopted, the atmosphere will remain to some extent polluted, if the room and its occupants are dirty. In certain experiments made by Carnelley in schools, it was found that dirty children increased the number of micro-organisms per litre of air more rapidly than dirty rooms. Thus:—
| DEGREE OF CLEANLINESS OF | CLEAN. | MEDIUM. | DIRTY. |
|---|---|---|---|
| Children | 63 | 99 | 159 |
| Rooms | 85 | 94 | 139 |
Number of micro-organisms per litre of air.
Hence cleanliness of rooms and of their occupants is quite as important as a good system of ventilation.
[CHAPTER XXIII.]
VENTILATION BY THE INTRODUCTION OF WARMED AIR.
Ventilation by the Burning of Coal. In winter and at any time of the year when the out-door temperature is below 50° Fahr., the warming and ventilation of a room are necessarily combined. If air is admitted unwarmed it will produce draughts, unless directed upwards by Tobin’s tubes or otherwise. In dwelling-rooms such contrivances may suffice; but in any larger building, in order to ensure sufficient ventilation, it is necessary to warm the incoming air.
The Open Fire-place forms the most common means of ventilation by heat (see also page [159]). The ascent of warm air up the chimney, causes cold air to rush along the floor to the fire-place from all parts of the room, especially the door. Part of the air thus approaching the fire is carried up the chimney with the smoke, while the remainder, after having been warmed, flows upwards towards the ceiling near the chimney-breast. It passes along the ceiling, and cooling in its progress towards the opposite wall, descends, and is again drawn towards the fire-place. Thus there is a continuous circulation of the air in a room.
In the experiments of the Barrack Commissioners (1861), it was found that the amount of air passing up the chimney while a fire was lit, ranged from 5,300 to 16,000 cubic feet per hour, the mean of 25 experiments being 9,904 cubic feet. We may conclude, then, that with an ordinary grate, a chimney provides outlet for impure air sufficient for four or five persons. Its lack of economy as a heat-producer will be considered later. Its efficiency as a ventilator within the above limits is evident.
When a fire is burning in the grate, all other openings in the room, except openings into the chimney, serve as inlets. If the room is insufficiently supplied with openings, a double current may be established in the chimney, with the result that occasional down-puffs of smoke occur.
As a rule the chimney serves only as an outlet for impure air. It may by appropriate means be made to serve as an inlet for pure and warmed air, the heat which would otherwise escape up the chimney being utilised for this purpose. Galton’s stove is one of the best for this purpose. At the back of this stove is an air-chamber, communicating with the external air, and in which the fresh air is heated before it enters the room. On the back of the stove broad iron flanges are cast, in order to present as large a heating surface as possible. They project backwards into the air chamber; and their heating surface is aided by the iron smoke-flue, which passes through the air-chamber. The warmed fresh air enters the room by a louvred opening above the mantel-piece, or by an opening in each side of the chimney breast. By this stove one-third of the total heat of the fire is utilised, as against one-eighth in an ordinary fire-place.
Fig. 16.
Vertical Section through Two Rooms, showing—A. Currents of cold air with an ordinary fire; B. Direction of currents of warmed fresh air with a Galton’s Ventilating Stove.
Shorland’s Manchester and other stoves are constructed on the same principle as Galton’s.
The Ventilation of Mines is effected by lighting a fire at the bottom of a shaft. The air for the combustion comes down another shaft (the intake shaft), or down another half of the same shaft separated by a partition. The consequence is that constant up and down currents of air are produced. The air from the intake shaft is made to traverse the galleries of the mines, its course being directed by partitions, before it is allowed to reach the fire and s be carried up out of the mine.
In addition to, or instead of, an ordinary coal-fire, the power for extracting impure air may be obtained from Hot Water or Steam Pipes. There are various plans founded on this principle.
When hot-water pipes are used for baths, etc., they may also be utilised for ventilation, in two ways:—1st. The hot-water pipe may be made to coil round the tube by which fresh air is admitted into a room, thus warming the air as it enters. 2nd. The hot-water pipe in its course upwards may be enclosed in a shaft, which opens into the external air above. The air in this shaft being heated, the impure air may be collected and removed from the different rooms by tubes connected with it. Thus, a hot-water apparatus, when well arranged and complete, may furnish pure warm air, and carry away impure air. The ventilation by this plan is found in practice to be somewhat irregular.
The plan proposed by Drs. Drysdale and Hayward of Liverpool is similar in principle:—Fresh air is warmed by a coil of hot-water pipes in the basement, and is admitted into the staircase and landings, when it is supplied to the different rooms by openings provided with valves. From the rooms, special outlets converge to a foul-air chamber under the roof. This is connected with a shaft leading from the kitchen-fire, the latter, therefore, acting as an extraction furnace.
Lighted Gas may be employed to produce a current for ventilating purposes, as well as fire or hot-water.
Sunlight and Benham’s Ventilating Gas-burners, have already been mentioned in this connection (page [149]). They are extremely valuable means of ventilation, producing powerful currents of air from all quarters of the room unless they are specially enclosed.
In theatres and similar buildings the Chandeliers may be made to extract vitiated air. Where a number of chandeliers exist, they may be connected by tubes with a main shaft, and all made to contribute to the same object. According to the experiments of General Morin, the discharge of 1,000 cubic feet of air is produced by the combustion of one cubic foot of gas.
Various forms of gas-stoves are now sold, which act as ventilators as well as sources of heat. Among these is George’s Calorigen Stove (Fig. 17). It can be obtained in various forms suitable for burning coal-gas, or coal, or oil. Within its outer case is contained a special iron tube, which communicates at its lower end with the outer air, and opens at its upper end into the room. The heat generated in the stove warms the air in the spiral tube, which accordingly ascends into the room. The ascent of warm air causes a draught from below, and the consequence is, that so long as the combustion is going on, a current of warm air continues to ascend into the room. The products of combustion are carried out of the room by the pipe F. This stove is free from most of the objections appertaining to gas-stoves; it can be fixed into an ordinary fire-place, and made to keep the temperature of a room uniform.
Fig 17.
George’s Calorigen Stove.
- A—The interior of the room.
- B—Exterior of building.
- C—Wall.
- D—The Calorigen.
- E—A cylinder.
- FF—Pipes communicating with stove and cylinder to supply air for combustion, and to carry off the products of combustion.
- G—Pipe for passage of fresh cold air to Calorigen. Can be carried above the floor between the joists, as may be more convenient.
- H—Outlet for air into the apartment after being made warm.
Bond’s Euthermic Stove is similarly constructed to the above, but is open below so that the air needed for the gas combustion is drawn from the interior of the room, and the continuous change of air is thus favoured.
Objections to Ventilation by Heating Apparatus.—When warmed air is admitted into a room, it is very apt to be dry and irritating. This can be usually avoided by having water standing in the room, so as to allow evaporation. A more difficult problem is to ensure the complete absence of all products of combustion, particularly of the products of incomplete combustion.
[CHAPTER XXIV.]
THE WARMING OF HOUSES.
Physiological and Physical Considerations.—The warmth of our bodies is naturally kept up by the oxidation changes constantly going on in the system. In Chapter XL., p. 265, are discussed the modes in which heat is lost by the system, and the influence of clothing in controlling the amount of this loss. Artificial warming of houses has a similar action to clothing. It diminishes the demand on the system, and so economises the amount of food required.
The degree to which this diminution of loss of heat by clothing and artificial warming of houses may be carried varies with circumstances. There can be no doubt that if food be abundant, exposure to external cold, if not too extreme, is on the whole beneficial, for vigorous people. But for old people and young children, means of artificial warmth require to be more carefully provided. Severe cold is for them often the harbinger of death.
The Degree of Temperature at which living-rooms should be kept will vary with circumstances.
For healthy adults, any temperature between 50° and 60° Fahr., will be moderately comfortable; for delicate children and old people it may be 65° with advantage.
For sick rooms and hospitals the temperature of 60° is usually adopted, but this is by no means always necessary. A temperature of the room as low as 50°, except for such diseases as whooping cough and bronchitis, suffices if the patient is well covered with warm personal and bed coverings.
Convalescents from any acute illness bear low temperatures badly.
The Different Kinds of Heat.—Heat may be communicated by radiation, conduction, and convection. By radiation of heat is meant the process by which heat passes from a fire or other source of heat, through a vacuum, dry air or any other medium, without heating any of the media through which it passes, but only the bodies against which it finally impinges. The solid bodies (including ourselves) which are warmed by radiant heat, by a process of conduction then warm the surrounding air. This method is the nearest imitation of the natural warmth of the sun.
Conduction of Heat is the passage of heat from one particle to another, whether it be of a gas or solid. It is an extremely slow process when air is concerned, and may be practically ignored.
Convection of Heat is the process by which a gas or liquid actually carries the heat in itself from one part to another. The heated particles are relatively lighter, and ascend to the higher parts of a room, while colder and heavier particles descend, and are subjected to the same process. Heat can be carried by convection only by gases and liquids. It is quite possible, therefore, for a person to be cold in a room filled with warm air, if the walls, etc., are cold; and on the other hand, to feel comparatively warm in a room filled with cold air, if more heat is radiated from an open fire-place or the warm walls to his body than he radiates to his surroundings. The feeling of “draught” when sitting near a wall is sometimes caused by radiation of heat from the body to the colder wall. The ideal arrangement, were it practicable, would be to have cool air to breathe, but to be surrounded by warm walls, floors, and furniture. A room warmed by an open fire is more comfortable than a room warmed by hot air from a furnace, assuming the temperature of the air is the same in both instances, because the walls of the room are several degrees lower in temperature in the latter than in the former. For warming walls as well as the air high pressure steam pipes are more efficient than hot-water pipes. The great advantages of radiant heat are that—(1) it heats the body without appreciably heating the air; while at the same time (2) there is no possibility of impure gases being added to the air.
It has, however, considerable disadvantages. (1) It is costly, though its expense may be greatly diminished by a well-constructed fire-place. (2) It only acts on bodies near it to any useful extent. Its effect lessens as the square of the distance; thus, its warming effect at five feet distance, is twenty-five times less than at a distance of one foot. It is evident, therefore, that for long rooms, and for large assembly-rooms, a single source of radiant heat is quite inadequate. The immense loss of heat in our ordinary fire-places is slowly leading to their modification; and although it is probable that radiant heat will always be the favourite source of warmth in dwelling-houses, it will be used for larger buildings chiefly as an adjunct to convection of heat.
The different sources of heat are employed, either singly or combined, in the following methods of warming our dwellings and other buildings:—
- 1. Warming by the open grate.
- 2. Warming by closed stoves.
- 3. Warming by hot-water pipes.
- 4. Warming by steam in pipes.
- 5. Warming by hot air.
- 6. Warming by electricity.
Warming by the open Grate.—In the open fire-place radiation is the source of heat chiefly employed.
The position of the fire-place is important. It should not be on the external wall of the house, as thus a large proportion of heat is lost; but should be placed where the heat from the flue may be utilised in keeping up the temperature of the house.
The construction of a fire-place is commonly faulty in several respects. (1) The fire-place may be too far included in the wall, so that the heat at once passes up the chimney. (2) It may be composed chiefly of iron, which rapidly conducts away the heat, and does not furnish a surface for radiation. (3) The bars and bottom of the grate may be so arranged, that coal and cinders fall out in an incompletely burnt condition.
It has been estimated that with an ordinary fire-place, seven-eighths of the possible heat is lost, one-half being carried up the chimney with the smoke, one-quarter carried off in the ascending current of warm air, and one-eighth of the combustible matter remaining unconsumed, forming the solid matter of the smoke.
The defects which have been indicated may be remedied by bringing the fire-place rather further out into the room; by substituting fire-brick for iron behind and at the sides of the fire, and by having a layer of fire-brick at the bottom of the grate, or the grate lowered, so that as in Teale’s stove, it lies on a bed of fire-brick at or below the floor level.
The shape of the grate is important. The width of the back of the grate should be about one-third that of the front, the sides sloping out towards the front of the recess. The depth of the grate from before backwards should be equal to the width of the back. The sides and back of the fire-place must be made of fire-brick, thus ensuring the heat being retained in the grate. And finally, the chimney throat must be contracted so as to ensure more complete combustion. The chief objections to an open fire-place are (1) the great waste of fuel involved, even after the improvements indicated have been carried out. (2) The unequal heating at different distances from the fire. (3) The smoke and dust always produced to some extent, from accidental smoking of the fire, or from the escape of ashes. (4) The trouble involved in frequently replenishing the fire. (5) The cold draughts produced by the currents of air towards the chimney. These travel chiefly along the floor, when, as is commonly the case, the space between the bottom of the door and the floor forms the chief place for the entry of fresh air.
Many patents have been brought out for the introduction of the fuel at the lowest part of the fire. The uppermost part of the fuel being first burnt, and the remainder attacked from above, the smoke is consumed in passing through the red part of the fire. Thus a comparatively smokeless fire is produced, and the amount of heat evolved is greatly increased. So far none of these have been altogether satisfactory. The production of a comparatively smokeless fire is a great boon. Smoke means so much unburnt fuel, and not only so but the sooty particles float about in the atmosphere, rendering it impure, and changing comparatively harmless mists into town fogs, which are loaded with soot and the products of combustion, and do incalculable mischief to health and property. The prevention of this smoke nuisance demands more consideration than it has yet received. The Public Health Acts constitute the emission of black smoke from the chimneys of manufacturing premises a nuisance; and manufacturers can if they use proper boilers, especially those in which mechanical stokers are employed, almost completely obviate this nuisance. The great principle is to prevent the escape of smoke before it is completely burnt. This may be accomplished by careful stoking, by keeping the unburnt coal at the front of the fire, and by ridges exposing the smoke to red-hot fire-clay before it escapes. In domestic fires, gas is gradually replacing coal for cooking, with a corresponding reduction of the smoke-nuisance.
The Utilization of the Heat Produced in the fire-place to warm the air on its way into the room, as in Galton’s and other similar stoves has been already described (page [156]).
A larger amount of heat can be obtained out of a given quantity of fuel by cutting off some of the cold air, which rushes through the fire, and carries the half-burnt gases and much of the heat up the chimney. This is effected by having a solid fire-brick bottom to the grate, or by closing up the front of the open chamber under the grate, by means of a close-fitting shield or door. These “Economisers,” as Mr. Teale calls them, appear to answer better than solid fire-brick bottoms, as they do not prevent the ashes falling under the grate.
The Fuel burnt in an open fire-place may be either coal or coal-gas. Occasionally coke is also employed. Coke and coal-gas have the advantage over coal, that (1) no smoke is produced. Coal-gas presents the additional advantages, that (2) it can be turned on at any moment, without having to go through a tedious process of lighting the fire; and that (3) the amount of heat can be exactly graduated by regulating the supply of gas. A gas fire is however, as a rule, more expensive than a coal fire.
Open Gas-stoves are made in various forms. In the common one, small jets of gas are lit under the grate, which is filled with pieces of asbestos. These become red hot, and radiant heat is emitted. To obtain the greatest value from the heat generated by the combustion of gas, a stove should be chosen in which the heat generated is brought into contact with a large surface of the grate before the products of combustion are allowed to escape to the flue.
Gas stoves which are advertised as not needing a flue, should be avoided. A large amount of carbonic acid is discharged by them into the room, and the sulphurous acid also produced by the combustion of gas is not completely absorbed in the water of condensation which collects in a tray under such stoves.
Closed Stoves form the most economical and efficient warmers for rooms of moderate size, and coal, coke, coal-gas or paraffin may be burnt in them.
The advantages rightly claimed for coal stoves of this type are that (1) the amount of fuel consumed is small; (2) by adjusting the damper, combustion may be rendered as slow as desired, so that but little heat is lost by the flue or chimney; and (3) heat radiates from all parts of the stove into the room, and not simply from a small area of fire-front.
The chief objections to closed stoves are, that (1) they dry the air excessively, rendering it somewhat unpleasant. (2) They produce a peculiar close smell, apparently caused by the charring of minute particles of organic matter in the air, coming in contact with the stove. If the air of the room is not heated above 75° Fahr., no smell is produced, and the relative humidity is not lessened to any appreciable extent (Parkes). But when the heat produced by the stove is excessive, these results do follow. The unpleasantness may be modified though not entirely removed, by placing shallow pans of water near the stove.
(3) Portions of the products of combustion may pass through cracks or fissures in the stove, or even through the joints of the stove. Independently of such accidental cracks, cast-iron stoves, when red hot, appear to allow gases to pass through them with comparative ease. Thus carbonic oxide and other gases may find their way into the room, and it is probable that this rather than the dryness of the air, is the cause of the unpleasant symptoms sometimes complained of in rooms where closed stoves are in use. This escape of carbonic oxide does not occur with earthenware stoves properly encased with fire-clay.
Fig. 18.
Slow Combustion Stove.
Many modifications of the older closed stoves are now in common use. In the stove shown in Fig. 18, excessive heating of the air is prevented by the presence of two air chambers, only the outer one, which brings external air to be warmed, having its air emptied into the room.
Warming by open grates or closed stoves is specially applicable to the rooms of private houses; warming by hot air or steam, or hot water, is chiefly used for large buildings. It is quite possible that these methods will be applied at some future time on a large scale to the warming of private houses. In some large towns of the United States this has been already done, blocks of a hundred or more houses being warmed from the same centre, by the same system.
But apart from such a central system, hot air and hot water lend themselves to the heating of houses on what may be called the Whole House System (page [156]). We have mentioned in the last chapter some methods of doing this, and shall now describe others.
Hot-water Pipes are probably the best means of carrying heat to various parts of a large house, and hot water is more thoroughly under control and less dangerous than either hot air or steam. There are two systems of heating by hot water.
In the first, which we may call the low pressure system, there is a boiler from which water circulates through pipes to every part of the building, and as it cools down returns again to the boiler. At the highest points of the pipes, outlets are provided for air. In this system the water is not heated above 200° Fahr., and there is consequently no great pressure on the pipes.
In the high pressure system (Perkin’s patent), the pipes have an internal diameter of about ½ an inch, and have thick walls made of two pieces of welded iron. There is no boiler, but one portion of the tube passes through the fire and the water is heated to 300-350° Fahr., thus subjecting the pipes to great pressure. In dwelling-houses with the low pressure system, for every 1,000 cubic feet of space to be warmed to 50°, 12 feet of 4-inch pipe should be given; with Perkin’s pipes, probably about two-thirds of this will suffice.
Steam Distributed by Pipes may be employed instead of hot water. This method has been used in factories in which there is a surplus supply of steam.
Warming by Hot Air is only applicable on a large scale, and should only be used in association with a system of ventilation by propulsion (page [153]), in which the temperature, humidity, and freedom from dust of the entering air are carefully regulated.
Warming by Electricity both for cooking food and for warming rooms has a large future, but in most districts the supply of electricity is not hitherto sufficiently cheap to be used for these purposes. By its means the atmosphere will be prevented from becoming impure, labour will be reduced, and life rendered more pleasant.
Hot Water Supplies.—Nearly every modern house is supplied with a bathroom, and this may be supplied with hot water either from a geyser or from the kitchen boiler. In a geyser the water is made to flow over a large heating surface furnished by burning coal-gas, and with the best varieties a bath of 98° F. can be supplied in from five to ten minutes. As the bathroom is usually small and unprovided with an open fire-place, persons have occasionally been suffocated by remaining in such a room while the gas continues burning. This is due to the production and in-breathing of carbonic oxide. No geyser ought to be allowed to be used which is unprovided with a flue passing into the chimney flue or in its absence through an external wall of the house. Short of fatal poisoning, violent headaches often occur when a warm bath obtained by means of a geyser is taken, unless such a flue is provided. In Ewart’s lightning geyser, additional protection is furnished by the fact that a dual valve is so arranged, that immediately the water is turned off or the supply fails from any cause, the supply of gas is also cut off.
Hot water supplies from kitchen boilers, unless carefully arranged, may be responsible for serious explosions during severe frosts.
Four plans are in common use. (1) The worm-boiler system. This system is unsafe unless the supply of water to the boiler is attended to; and as the hot water supply to the kitchen is drawn from the boiler itself and not from the worm, the hot water supply for the rest of the house may be deficient. Usually the small feed cistern for the boiler in this system is too near the boiler to freeze.
(2) The cylinder system is very effective. In this system a metallic cylinder, capable of withstanding a pressure of 20 lbs. to the square inch, is placed in the kitchen or bathroom between the cold and hot supplies, its contained water being heated by circulation from the boiler, hot water ascending and cold descending. On the top floor of a house is a cistern from which cold water is supplied. Both the supply pipe and escape pipe for hot water may become frozen during frost. Then the supply of water is stopped, and the boiler and reservoir may boil dry. This would not occur without some indication in unusually vigorous boiling. Boilers sometimes explode, and cylinders sometimes explode. This can be effectually prevented by (3) A Double-cylinder apparatus one within another. In this the water in the outer cylinder supplied from the main cistern can only be heated to 212° F., and the water in the boiler and inner cylinder supplied from a lower feed cistern can only be heated to 214° F., on account of the small head of water. Two escape pipes give free communication with the atmosphere. (4) In the tank system, which being cheap, is usually adopted in poor houses, the tank is placed high up in the system. The hot water branch pipes are usually taken from the flow-pipe between the boiler and tank. Hence when the supply fails, as during frost, the tank is drained empty, the circulation of water ceases, and the system is changed from a circulation system to a high-pressure one.
Safety valves cannot always be relied on to prevent explosions. If they lead to the lighting of fires in frosty weather, when pipes are frozen, they may cause explosions. Explosions from frost only occur when both pipes are blocked. Incrustation of the boiler and pipes increases the danger of explosions; hence the necessity for their periodical cleaning.
[CHAPTER XXV.]
HOUSE DRAINAGE.
The Removal of Impurities.—In order that health may be maintained in any inhabited house, it is essential that the impurities produced by animal life should be removed. These impurities may be divided into two classes—the first including the gaseous and volatile products evolved from the lungs and skin; and the second, the liquid excretion from the kidneys, and the solid from the bowels. The former are got rid of by efficient ventilation and by cleanliness; the latter, ought to be as quickly removed, but require more elaborate arrangements to ensure this.
The average daily amount of solid excreta is about 4 ounces, and of fluid excreta about 50 ounces for each adult male. Taking all ages and both sexes into consideration, the amount per head is about 2¾ ounces of fæces and 32 ounces of urine. When dried, the daily fæces amount to 1·04 oz., the daily urine to 1·74 oz., so that the manurial value as well as the possible polluting power of urine is much greater than that of the fæces.
After a variable interval urine and fæces begin to decompose, ammonia and fœtid gases being disengaged in large quantities. Urea the chief constituent of urine is decomposed into carbonic acid and carbonate of ammonia. Thus
CH₄N₂O + 2H₂O = (NH₄)₂CO₃
In addition to the excreta, house-slops have to be got rid of, and “dust.” House-slops vary greatly in quantity, but probably amount to as much as sixteen gallons per head daily. They consist chiefly of the water used in cooking and washing and for baths. It would be a mistake to suppose that only urine and fæces need careful disposal. There are masses of decaying epithelium from lavatories and baths, organic matters from soiled apparel, and various organic matters from culinary operations, all of which may cause serious nuisance unless promptly disposed of.
The Dust consists chiefly of the ashes from fires; but the dust-bin also forms a favourite refuge for kitchen refuse, composed of various animal and vegetable matters, as well as for broken pots and tins. It is dealt with apart from the house-slops and excreta, except in certain dry methods of disposal of sewage.
Two chief plans of getting rid of the sewage have been proposed, though there are many varieties of these. They are—
- 1. The Water Method, and
- 2. The Dry Methods.
For towns the water carriage of sewage is indispensable, and in this chapter we shall confine ourselves to the part of this system which relates to the Drainage of the House.
The chief sanitary appliances of a house, which empty their contents into the drain and thence into the street sewer, are—(1) Rain-water Pipes; (2) Bath-room and Sink-pipes; (3) Water-closets; (4) Soil-pipes; and (5) The House Drain. We will consider these in detail.
Rain-water Pipes collect the water from the roof by means of gutters, and carry it down to the house drain, except in the few cases in which the rain-water is collected for use. The rain-water or stack pipe was formerly joined directly at its base with the underground drain. This was evidently bad, because the upper end of the pipe was frequently near windows, and foul gases from the drain might be conducted by it into the house. It is equally objectionable to connect the rain-water pipe with the soil pipe and for the same reasons as above.
The general rule with regard to all pipes carrying away water from the house, with the sole exception of the soil-pipe, is that they must be disconnected from the underground drain and discharge into the open air over a gulley-trap. This rule applies to
- rain-water pipes, and to
- waste pipes from baths,
- lavatories,
- sinks.
It does not apply to the soil-pipes leading from
- water-closets and
- slop-sinks,
Overflow or waste-pipes from cisterns for drinking water or from cisterns for flushing w.c.’s or to safe trays under the seat of water-closets should all be made to discharge into the open air, where the leakage can at once be discovered.
The form of gully-trap to be used at the junction with the drain is described on page [167].
Other Waste-pipes as from bath, lavatories, and sinks, must be similarly disconnected from the drain, and made to discharge over gully-traps. When the pipe leading from the bath, lavatory basin, or sink, is long, it is apt to become foul from the accumulation on its inner surface of slimy matter, consisting of soap, dirt, and other offensive matter. For this reason it is wise to have a syphon bend in the waste-pipe near its junction with the sink or basin. Such a trap is shown in Fig. 19.
The syphon bend alone in the waste-pipe without disconnection from the drain at its lower end would not suffice to ensure complete absence of nuisance, especially for sinks and lavatories which may be disused for a considerable period. Under these circumstances the water in the syphon trap may become evaporated, and then foul drain gases be wafted into the house. Furthermore, even if the water in the syphon trap remained, foul gases may be absorbed from the drain and given out at the end nearest the house (a, Fig 19). Hence it is always best to disconnect all waste-pipes from the drain, except the soil-pipe which cannot be treated in this way. The waste-pipe from the upstairs lavatory or bath may be made to discharge over a hopper-head and thence into the rain-water pipe, which is disconnected below from the drain. This plan should only be adopted when the hopper-head is not close to a bedroom window.
Fig. 19.
Syphon Trap under Sink, with Screw-opening for Cleansing.
Under the bath is usually placed a leaden tray, called a safe, to catch any accidental spillings of water. The overflow pipe from this safe should discharge direct into the open air. Formerly much evil was caused by allowing waste-pipes from baths, sinks, and lavatory-pipes, or overflow pipes from drinking-water cisterns or from the bath-safe, to be connected directly either with the trap of the w.c., or with the soil-pipe beyond it.
Fig. 20.
| A Stoneware Gully-trap. | B Section of the same, showing a Water-seal 3 inches in Depth. |
Sinks are not uncommonly the source of offensive smells, when made of wood or stone. A hard glazed sink should be provided; as this is non-porous and can be kept clean. The sink should be placed against an external wall, so that the waste pipe can be carried through the wall to a gully-trap outside the house. Formerly the sink-pipe was joined below directly into the drain, the only obstacle to the entry of sewer or drain gases into the kitchen being a bell-trap at the sink. This is quite insufficient for the purpose. The waste-pipe from the sink should have a syphon trap under it, with an inspection opening at its lowest point (Fig. 19), and should discharge in the open air over a gully-trap (Fig. 20), as in the case of rain-water and bath-waste pipes. It is usually stated that the waste-pipes from sinks, etc., should discharge at least 18 inches distant from the grating of the gully. This is too far, because some of the foul water may become dried up in the channel, and its solid particles be blown about. They may be allowed to discharge directly over the grating of the gully (Fig. 20) or even into the side of the gully below the grating, but above and on the house side of the water-seal shown at B. Fig. 20.
The gully-trap is connected with the socket of the first drain-pipe, and the junction is made water-tight by means of a cement joint. On this account, and because it gives a better water-seal than the bell-trap or D trap, the gully-trap should be always used. The best form of gully-trap, the P trap, is shown in Fig. 20 B. This is better than the S trap (Fig 19), which involves a bend in the drain at its junction with the trap.
Water-closets require to be skilfully constructed and well-situated, if they are not to become a serious nuisance. In building a house, the position of the closet should be carefully considered. In all cases it should be in an out-standing part of the house, against an external wall, and separated from other parts of the house by a passage, preferably a passage which is cross-ventilated. Instead of this, one commonly finds it in any convenient recess, abutting on a bedroom, or where it cannot be properly ventilated. Usually the closet is placed at the back of the house; and as the main-sewer is generally situated in the front street, it follows that the drain must in terrace houses pass under the house. Hence the importance of having it completely water-tight. Water-closets in bathrooms are very inadvisable.
The ventilation of the closet should be good—if possible, by two opposite windows; and where practicable a cross-ventilated lobby should intervene between the closet and the rest of the house. This is now always provided in hospitals.
The water-supply to the closet should be abundant. Every flush of water should be sufficient to carry the contents of the basin through the soil-pipe and the drain into the sewer. The quantity allowed by the Water Companies in London is two gallons, which is barely sufficient for this purpose, unless the form of closet pan is good, and the down-pipe to it of sufficient diameter. Each closet should have a separate cistern, the best being the so-called “water-waste preventer,” by means of which a certain quantity of water, and no more, can be discharged each time the handle is pulled. One of the best of these is shown in Fig 21. When the handle of this is pulled, the whole of the water in the cistern is syphoned out by the syphon and carried down to the water-closet, whether the handle be held down or not.
The amount of fall from the cistern to the closet should not be less than four feet, and the pipe should be free from bends in order to ensure a thorough scouring of the trap and soil-pipe; and the flushing-pipe should have an internal diameter of not less than 1½ inches. It is commonly supposed that a small flow of water, trickling continuously down a closet, tends to keep it clean, and prevent smells; but the water thus used is simply wasted. Others fasten up the handle of valve-closets so as to allow a large flow of water. This does not answer the desired end, and renders the offending person liable to a penalty for wasting water.
Many different forms of water-closet are in use. In all of them the main requisites are that there should be (1) a good flush of water, (2) a rapid removal of the excreta, and (3) no possibility of reflux of gases. The chief varieties of closets are the pan, valve, wash-out, and wash-down closets.
Fig. 21.
Syphon Flushing Cistern.
In Fig. 21 a portion of the bell of the syphon is shown cut out, so as to display the movable plug at the bottom of the cistern. An objectionable feature in most cisterns is their noisiness in use. In the above cistern, the pipe admitting water is carried down to within an inch of the bottom of the cistern, thus ensuring noiseless entry of water.]
Pan-closets (sometimes called double-pan closets) are essentially bad, though largely employed in the past. The construction is shown in Fig 22. Below the conical basin there is a metal pan capable of holding a certain amount of water, the lower end of the basin dipping into this water. By means of a pull-up apparatus the contents of the pan can be tilted into a second larger pan or container, and the bottom of the container is connected by means of a short pipe with a leaden [bowl-shaped symbol] shaped trap, from the side of which the soil-pipe passes out to be carried down to the drain. The arrangement insures the production of nuisance. The container and [bowl-shaped symbol] trap always arrest a certain amount of foul matter; and each time the handle of the closet is pulled up a puff of foul air comes into the operator’s face. Occasionally the [bowl-shaped symbol trap becomes corroded by the filth it contains, and foul gases from the drain escape into the house.
Fig. 22.
Insanitary Pan Closet, showing D Trap below.
Valve Closets differ from the last in having no container, but only a small box containing a movable water-tight valve, exactly fitting the lower edge of the basin (Fig. 23). They are much superior to the pan-closet, but require an overflow pipe in order to avoid accidental flooding of the closet. The overflow pipe should be made with a syphon bend in it, and the flushing of the closet should be so arranged that each time it is performed water enters the overflow pipe. (See Fig. 23.) The trap below the valve should be in the form of a syphon (see under traps, page [179]), as this is not easily fouled. It is preferably made of lead, securely jointed to the soil-pipe and to the valve box of the closet. A lead tray or “safe” is required on the floor beneath a valve closet, in view of accidental spillings or overflow; and this should be provided with an overflow pipe discharging into the open air.
Fig. 23.
A—Pan. B—Overflow pipe with syphon trap. C—Valve shut. C1—Valve open. D—Valve box. E—Floorline. F—Water-seal of trap.
Valveless or Hopper Closets, of which the Wash-out, Wash-down and Syphonic Closets, are the chief forms, present certain advantages over the valve closet. There is less apparatus to get out of order and no metal to become foul. They do not require an overflow pipe, as water can escape freely through the trap of the closet. Valveless closets need not be encased by wood-work, thus ensuring freedom from spillings of foul water, and they are more easily used than valve closets for the discharge of bedroom slops, thus obviating the necessity for a special housemaid’s sink. Valveless or hopper closets are cheaper and simpler in use than valve closets, and when in use are equally sanitary. If a house is left empty for a considerable time, the water in the trap may, however, become evaporated, an event much less likely to occur with a valve-closet. The latter are furthermore less noisy when flushed. With a valve to hold up the water in the pan, as in the valve-closet, a much larger quantity of water can be retained than with a hopper closet. Hence the importance of the latter having such a shape as shall prevent fouling of the basin by fæces.
One of the older hopper closets was the long hopper shewn in Fig. 25. In this form the pan is conical in shape, its sides necessarily becoming fouled by its use, and the spiral flush, the point of entry of which is shewn in the figure is quite insufficient for cleansing the pan.
Fig. 24.
Rim Flushing Wash-down Basin.
Of Short hoppers the best has a nearly vertical back as shewn in Fig. 24, a rim-flush, by means of which at least two gallons of water are discharged with the fæces, and the pan is thoroughly cleansed.
The wash-out closet is shewn in Fig. 26. In it a certain amount of water is kept in the upper part of the pan by a ridge over which the fæces have to be driven before entering the trap. The force of the flush is thus broken. In this closet a large area is liable to be fouled, and it is now almost entirely disused.
Fig. 25.
Short Hopper Closet. Long Hopper Closet with Spiral Flush.
Syphonic water-closets are wash-down closets, in which the flushing out is aided by syphonic action. They need to be fitted with a flushing cistern, giving an after-flush as well as a flush; otherwise the basin is left untrapped. One of the most elaborate closets of this type is Jennings’ Closet of the Century. Fig. 27 shows that the flushing cistern has two connections with the closet, one in the usual manner with the flushing rim of the pan, the other connected to the long arm of the syphon (A Fig. 27). B is a puff pipe allowing the escape of air from this syphon when started. Thus while one part of the flush scours the basin, the other expels the air from A through the puff-pipe B, fills both arms of the syphon with water, and thus starts the syphonic action by which all the contents of the basin are sucked out of it. In this form of w.c., syphonage is intended to be produced, and the after-flush prevents the w.c. from being left untrapped.
Fig. 26.
Wash-out Closet.
Syphonic water-closets appear to me to be unnecessarily elaborate and complicated, and the only advantage over the wash-down closet is the deeper layer of water in the basin. With a well-shaped wash-down closet this is of little importance.
Fig. 27.
Syphonic Closet.
In other forms of wash-down w.c., unsyphoning may also occur, for instance, by pouring the contents of a slop-pail into the pan. This is particularly apt to occur, when two or three water-closets are on different floors of a house, one over another. This unsyphoning is prevented in the case of the highest w.c. by the soil-pipe ventilator, but not always for the lower w.c.’s. For these it may be necessary to carry a pipe from the highest point of the trap of the closet, where it joins the soil-pipe, through the wall into the external air. Such a pipe is called an anti-syphonage pipe (Fig. 28). It effectually prevents the water being sucked out of the trap of a lower w.c. when the w.c. on a higher floor is being flushed.
AFig. 28.B
A—Elevation. B—Section through wall of house, showing connection of w.c.’s on three floors, with soil-pipe and anti-syphonage pipe. b—Junction of closet trap with soil-pipe, a being a P and b an S trap. c—Junction of soil-pipe with earthenware drain. d—Anti-syphonage pipe, seen best in elevation A. e—Soil-pipe. f—Anti-syphonage pipe. g—Underground drain. h—Soil-pipe ventilator. i—Cage-work protecting top of h. j—Point at which anti-syphonage pipe is connected with soil-pipe ventilator, above the highest w.c.
In the forms of w.c. already described, clean water is used for flushing, and we have seen that two gallons, the quantity usually allowed, does not suffice for this purpose, unless the closet pan is of the best possible shape, and the service pipe sufficiently wide to project the water by means of a rim-flush forcibly over the pan and into and beyond its trap. Other forms of w.c. have been employed of which the most important are slop-water closets, and trough-closets.
In Slop-Water Closets the waste water from sinks and baths is utilised for flushing, and thus a saving of water is effected. This form of closet is used considerably in manufacturing districts, and is less liable to freeze than an ordinary w.c. The sink discharges on to a gully in the usual manner, but the outlet of this gully is connected with a tilting vessel or tipper, holding 3½ gallons in Duckett’s closet, which is the best known of this type. The tipper is balanced on brass bearings, and tips over when full, discharging its contents into the closet trap, which is thus flushed. The slop-closet is a great improvement on the privy-middens or pail-closets, which in some towns it has superseded, but is not so cleanly as an ordinary w.c.
Trough Closets are also known as “latrines.” The best type consists of a glazed earthenware trough under a series of w.c. seats. The trough is slightly inclined towards the outlet, at which is a weir, beyond which is a trap. An automatic flushing tank connected with the upper end of the trough and five to six feet above it, discharges water at intervals and drives the fæcal matter over the weir and through the trap. This form of closet is only suitable for factories. It is to be deprecated for schools, and even for factories, unless there are exceptional reasons for its continuance, as fæcal matter possibly of an infectious character may be retained a considerable time in the trough.
The domestic Slop Closet or “housemaid’s sink” must not be confused with slop-water closets mentioned above. The slop-closet or sink is used for emptying the contents of bedroom pails. These being necessarily foul and liable to early putrefaction must be treated exactly like other sewage matters. An ordinary pedestal w.c. with a lift-up seat answers excellently as a slop-closet; but in large houses and public establishments a separate slop-sink is desirable with a larger surface than most water-closets. The slop-closet must be connected with the soil-pipe, just in the same way as a w.c.
Fig. 29—Section through a House from Front to Back shewing Drainage Arrangements.
A.—Sewer; B.—Intercepting trap; C.—Cleaning eye for pipes between chamber and sewer; D.—Inspection chamber; E.—Inlet ventilator; F.—Gully-trap for forecourt; G.—Air-bricks for ventilation under floors; H.—Damp-proof course[8]; I.—Concrete 6” thick over site of house; J.—Drain, fall 1 in 24, imbedded in concrete; K.—Soil-pipe carried up full size above eaves; L.—Upstairs w.c.; M.—Gully-trap receiving water from N scullery-sink, O bath and P rain-water stack-pipe; S.—Ventilating pipe at upper end of drain; T.—Pipes leading to same.
The soil pipe is the vertical pipe carrying the contents of the water-closets in the drain. It must be distinguished from the drain, which is chiefly, if not entirely, underground. The exact position of the soil-pipe and its relation to the drain can be seen in Fig. 28 and 29, which should be carefully studied. The soil-pipe should be made of drawn lead without seam, of uniform thickness throughout, and of at least 7 lbs. or better 8 lbs. weight per superficial foot. Any joints in the lead pipe should be of the kind known as “wiped,” not a “slip” joint. The outside of a wiped joint is shewn in Fig. 30B. Iron pipes if used must be 3 ∕ 16 inch thick, and have sockets sufficiently wide and strong to permit of the joints being caulked with molten i.e. “blue” lead, in the same way as water-mains are laid.
The soil-pipe should be throughout its course under observation. It should not be built into a wall, where it might be accidentally pierced by nails, nor within the house, allowing foul gases to escape from weak points in the joints. It should be carried through the wall of the house immediately beyond the closet trap.
The soil-pipe should not be more than four inches in diameter. It should be continued from its highest point at the junction with the closet-trap above the roof by a pipe of the same diameter, with its end wide open (Fig. 29 K). This ventilation of the soil-pipe is essential (a) to prevent the entry of foul effluvia into the house, especially when the water in the closet-trap is dried up; (b) to prevent unsyphoning of the upper by the lower water-closets in a house. (On this point see p. 172).
AFig. 30.B.
A.—Section showing a Good Method of connecting Soil-pipe to Drain by Brass Thimble.
B.—Outer View, showing Brass Thimble wiped on to Soil Pipe.
The upper end of the ventilating pipe should be made to open remote from any window. It may have a cowl attached to it, but it is doubtful if this materially aids the aspiration of foul gases. It is wise to cap the upper end of the ventilating shaft with a dome of large meshed wire-netting to prevent birds building their nests in it.
The connection of the soil-pipe with the closet-pan is its weakest point, and the most liable to leak. The main difficulty consists in forming joints between earthenware and metal. Socketed connections are not safe. The use of an india-rubber ring inserted between the lead and earthenware flanges and bolted together by means of a brass collar and hooked bolts makes a fairly good connection. Various screwed connections are made. In another form the earthenware collar is covered outside with lead, so that a soldered joint can be made between the earthenware trap and the soil-pipe. In the “metallo-keramic joint” the earthenware joint is painted over with a metallic solution and fired. To the metal film thus formed, lead or other metal can be firmly soldered.
The connection of the soil-pipe into the socket of the first pipe of the earthenware drain requires also to be carefully made. This pipe is curved, and at its upper end has a socket, into which the soil-pipe enters. A length of brass or copper tubing known as a “thimble” (about a foot long) should be soldered to the bottom of the soil-pipe; the rim of this thimble rests in the socket of the drain-pipe and the space between the two is filled with Portland cement (Fig. 30A). With the ordinary connection between lead soil-pipe and drain, the former is apt to become dented by blows, and the latter is very liable to be partially blocked by the dropping of cement inside the pipe when making the joint.
The House Drain under ordinary circumstances receives waste water from sinks and baths, rain-water, and the discharge from the closets.
Fig. 31.
Showing Depth of Fluid and consequent Flushing Force of Three Drains containing an Equal Quantity of Sewage.
We may consider drains under the following heads: material, form, joints, gradient, ventilation, trapping. The first essential is that they should be water-tight, so that their contents do not percolate into the surrounding soil. Socketed glazed stoneware pipes and iron pipes best fulfil this condition. The best material for making stoneware pipes is Devon or Dorset, or similar fine clay, which makes a very strong pipe. Tested pipes free from cracks and flaws must alone be used. The pipes should be laid in straight lines, each pipe being arranged with the spigot and not the socket end directed towards the flow of sewage. The fall should not be less than 1 foot in from 40 to 60. If the fall is less than this amount, artificial flushing from the upper end of the drain is necessary. Usually branch drains are made 4 inches in diameter, the main house-drain having a diameter of 6 inches. A larger size than this is seldom necessary. Thus if A, B, and C be three drains with an equal fall and conveying an equal amount of sewage, the rate of travel and therefore the flushing force will be greater, because the depth of the fluid is greater, in A than in B, and in B than in C. Small drains are more completely self-cleansing than large drains. The water-tightness depends on the character of the joints. In this respect iron drains present the great advantage over earthenware that there are fewer joints and that these can be rendered permanently water-tight without difficulty by being run with blue lead and well caulked. To render an earthenware drain water-tight, (a) it must be laid on a solid bed of cement concrete at least 6 inches thick, so as to prevent sinking, and under the house it should be covered with an equal thickness of cement concrete (I, Fig. 29). (b) The joints must be made with extreme care, the best Portland cement being used for the purpose. Clay is inadmissible, as the fibrils of tree-roots easily find their way through it. The inside of the joint must be raked by the workmen, before the next pipe is laid, to make sure that no fragments of hard cement are left projecting in its interior. Such projections are not uncommon causes of subsequent blockage. Various patent joints have been used, but they are no better than the above when properly laid. Just before the drain leaves the curtilage of the house and near its junction with the sewer, it is trapped, and on the house-side of the trap (E, Fig. 29) an inlet ventilator is provided. The general arrangement should be studied in Fig. 29.
Ventilation of the house drain from end to end is important, a free escape of foul gases out-of-doors being induced. The exit is provided by carrying the soil-pipe up full bore above the eaves, and remote from windows. One opening alone would not induce a current of air, and the other end of the drain being trapped from the sewer (B, Fig. 29) it is necessary to provide an inlet for fresh air at E. This may be placed a few feet above the ground or at the ground-level. Usually a mica-flap valve is provided at its upper end, which closes whenever a puff of foul air attempts to escape from the drain. The necessity for this is doubtful. Ordinarily air enters at the inlet and circulates through the drain, escaping at the upper end of the soil-pipe ventilator.
It has been advocated that the soil-pipe ventilator should form a means of ventilating the sewer as well as the house-drain, the intercepting trap in the latter (B, Fig. 29) being removed. This is inexpedient, an element of risk being introduced, in view of the possibility of the drain or some of the connections of internal sanitary fittings being defective.
Fig. 32.
Weaver’s Intercepting Trap.
The drain as ordinarily arranged is trapped from the sewer by an intercepting trap. This is not merely a trap, but a trap provided with ventilation at its end nearest the house. A form commonly employed is shown in Fig. 32. B is the junction with the house-drain, at D is the water-seal, while at C fresh air enters the house-drain. E is a cleaning eye, through which any chokage can be cleared towards A, leading to the public sewer. It is important that the intercepting trap should be accessible in the event of accidental stopping. This is provided by an inspection chamber or man-hole. This if close to the house is provided with an air-tight cover, the inlet ventilator being conveyed above ground to a convenient point. The man-hole itself is built with brick set in cement and lined with cement. Note that in the man-hole itself half-channel pipes convey the sewage instead of complete pipes.
Sometimes more than one drain-pipe converges to the same man-hole, and then a more elaborate arrangement than that shown in Fig. 29 is required, the branch-pipes converging into half-channel pipes in the man-hole.
Varieties of Traps.—Traps are placed at various points of the house-drainage system to prevent the admission of currents of foul air into the house. They are all constructed so as to intercept a water-seal between the drain and the house or yard at the upper end of the trap. Traps are placed in four positions in connection with the drainage of a house: (1) near the junction of the house-drain with the sewer; (2) under the pan of each w.c.; (3) in the open air at the ground level to receive waste water from bath, sink, and lavatory basin; and (4) in the waste-pipe close under the bath, sink, or lavatory, when the waste-pipe is long and apt to become foul; (5) inside sinks at the upper end of their waste-pipes.
Intercepting traps between the drain and sewer have already been described. They must always be ventilated (C, Fig. 32 and Fig. 29). A syphon shape with a water-seal of 3 inches is required, and the trap should be self-cleansing, that is, whenever the w.c. is used, the fæces ought to be carried beyond the intercepting trap into the sewer. Other forms of intercepting trap were formerly used, one of the worst of which is shown in Fig. 33. With such a trap as this, an accumulation of filth is inevitable.
Fig. 33.
Deep Dipstone Trap, with Accumulation of Filth in it.
A—Drain entering trap. B—Drain leaving trap. C—Dipstone.
Water-Closet and Slop-Closet Traps are of the syphon or anti-D type. The water-seal in these must be at least 3 inches deep, and the trap must be ventilated by an upright extension of the soil-pipe, otherwise the water in the trap may be syphoned out when the w.c. is used. Hellyer’s “anti-D” trap is a lead syphon trap, the calibre of which is diminished at its bent portion, while the portion of the trap nearest the soil-pipe or drain is square instead of circular. The constriction increases the force of the flush of water and thus cleanses the whole trap, while the square shape impedes the free flow of water, and thus diminishes the risk of syphonage. Various forms of trap are shown in Fig. 19 to 34. The most objectionable of these is the old-fashioned D trap (Fig. 22), the corners and angles of which become fouled, and consequently the lead becomes corroded.
Fig. 34.
Bad Form of Trap: Bell Trap. Bad Form of Trap: Antill Trap.
Gully-traps are placed in the yard, for the discharge over them of waste-pipes (Fig. 20). A complete disconnection from the drains is thus effected. Formerly bell-traps were used for this purpose. In the Bell-trap not much water can get through, the space A becomes blocked with dirt, the cover B is often taken off and lost, and then the drain is untrapped; and even without this, the water-seal is very slight, and the water quickly evaporates.
Traps under sinks, etc., have been already described (page [166]).
Traps were formerly placed at the upper end of the waste-pipe of the sinks when this was directly connected with the drain. Of these the Bell-trap and Antill’s trap were most common. The Bell-trap has been described above. In the Antill-trap the trap is not removable, and the water-seal is deeper than with a bell-trap. This trap is sometimes used instead of a gully-trap, but is not so good.
Efficiency of Traps.—Eassie has said “honestly speaking, traps are dangerous articles to deal with; they should be treated merely as auxiliaries to a good drainage system.”
(1) The trap may have been imperfectly laid to begin with.
(2) It may be emptied by evaporation.
(3) Unless the precautions already mentioned (pages 172 to 173) are adopted, the flushing of one trap may empty another.
(4) The water of the trap may become impregnated with foul gases, and these then escape on the house-side of the trap. When a sewer becomes suddenly charged with a large amount of water, as during heavy rain, sewer-gases may force their way through the intercepting trap. With a ventilated drain and soil-pipe these dangers are so small that they may be ignored.
Unsyphoning of traps has been already mentioned. It occurs particularly when there are several water-closets one over another, connected with the same soil-pipe. The method of preventing it is shown in Fig. 28.
The Examination of Drains and Sanitary Appliances.—This examination will involve the detection of (a) any deviations from the details of construction and ventilation of drain and soil-pipe, form of w.c., disconnection of waste-pipes, already insisted on; and (b) any defect or leakage in any part of these.
1. Testing of Water-closet.—The interior of the basin or pan may be painted with a mixture of lamp-black, size and water. If the usual flush applied immediately afterwards clears this off, the form of pan and the flushing power are satisfactory. By removing the wood-work around the w.c., leakage or spillings of slop-water around the w.c. can be detected.
2. Testing of the soil-pipe may be effected by one of the volatile tests named under the next heading. To give the test a fair trial, the upper end of the ventilating pipe should be temporarily sealed over.
3. Testing of the drain cannot be efficiently carried out unless access can be obtained to the drain near the sewer. In a properly constructed house-drain a man-hole is provided for this purpose. Two chief methods of testing drains and soil-pipes are in use, by smoke or volatile agents and by water.
The smoke-test consists in filling the drains with smoke, the assumption being that this will find its way through any faulty joint or trap, thus indicating the site of the defect. Various arrangements are employed for pumping the smoke into the drain from the combustion chamber of a pumping apparatus; or smoke is produced by means of specially prepared rockets. All outlets or ventilating pipes must be carefully stopped during the operation, and the place where the smoke is smelt will then indicate any leaky point.
Fig. 35.
Showing Stopper for Water-testing of Drains.
Drain grenades are largely employed for the volatile testing of drains, the essential constituent being phosphide of calcium. The grenade, which is attached to a piece of string, is passed beyond the trap of the w.c., and as the string unwinds the grenade opens and discharges its contents into the soil-pipe. Or a tablespoonful of strong oil of peppermint, mixed with hot water, is poured down the highest water-closet in the house. If this is smelt by another person in the lower closets, it indicates defective traps or soil-pipe.
All volatile and smoke tests have but a limited utility. They are useful in detecting defective joints in traps and in the soil-pipe. They may detect defects in an underground drain; but if no smell or smoke is perceptible when a drain is tested by this means, the drain may still be seriously defective. The only absolutely trustworthy test for drains is the hydraulic or water test. The lower end of the drain is stopped up by a suitable water-tight stopper. Then the drain is filled with water by means of a tap in the yard, the amount of water used being approximately estimated by the rate of flow from this tap. The drain is filled up to the level of the gully-traps in the yard. If it remains at this level for half an hour, the drain is sound. More often it leaks so rapidly that it will not fill, or the level of the water falls quickly after filling, and it is necessary to strip and repair, or more generally to relay the drain so as to make it water-tight.
Rats are an important indication of defective drains. The presence of rats in a house should always lead to a thorough investigation of its drains.
[CHAPTER XXVI.]
CESSPOOLS AND MAIN SEWERS.
The terms Sewer and Drain are used somewhat confusedly. The term drain should be used to designate the pipes bringing the sewage from the house into the street-sewer, or any pipes by which the subsoil is drained; the term sewer being confined to the trunk canals into which the house drains empty their contents.
Where the water-carriage system of sewerage is adopted, involving the use of water-closets as described in the last chapter, the sewage may be carried from the house either into cesspools or into the main sewer.
Cesspools are only permissible in isolated country-houses supplied with water-closets. They should always be situated a considerable distance from the house, and should be emptied at regular intervals, the sewage being placed in shallow trenches on the land.
The construction of the cesspool requires careful attention. Its walls should be of brickwork set in cement, lined inside with cement, and surrounded by clay puddle. The bottom should have a fall towards one side, where a pump can be fixed, to remove the more liquid contents. The depth of the cesspool should never exceed 7 feet. The drain emptying into the cesspool should be trapped and ventilated, near its junction with the cesspool; and the cesspool itself should be ventilated.
In connection with many old houses in towns, cesspools still exist, sometimes under the basement or near the house, and so built as to allow soakage in every direction. The surrounding soil becomes contaminated for a considerable distance, the water in any neighbouring well is tainted, or leaky water-pipes receive the soakage. The cleansing of cesspools is always a disgusting process, and even dangerous to the workmen employed. They incur the risk of suffocation, and are very subject to ophthalmia. To avoid these dangers a pump and hose connected with a partially exhausted barrel is employed, but even with this provision some nuisance arises. In the Bexley cart, which is used for this purpose, a hose is used to connect the cesspool with an air-tight cylinder in the cart, into which the contents of the cesspool are pumped.
A modification of the cesspool system, called the Pneumatic System has been proposed by Captain Liernur. In it the cesspool is not placed under the house or the courtyard of the house, but under the street at the angle of junction of several streets. It is made of cast-iron and air-tight, and is connected with all the houses of several streets by iron pipes. By means of a powerful air-pump worked by steam, the cesspool is emptied into barrels in which it is sent directly to farms; and the barrels being placed on ploughs of peculiar construction, the manure is discharged from the bung-hole of each barrel and covered over with earth in the progress of the plough. The pipes tend in this and similar systems to get clogged with fæcal matter, and large quantities of water are required to keep them clean, so that the system merges into that of the use of water-closets, but without the thoroughness of the latter.
Cesspools have been almost improved out of existence in some continental towns, by the introduction of movable cesspools,—fosses mobiles,—to which would correspond strictly the tubs and pails used in some of our large towns. Such movable receptacles have been still further “improved” by the adoption of separators, by which the liquid parts are allowed to escape into the sewer, while the solid parts remain comparatively inoffensive. But when this is done, the cesspool may be as well abolished, as the foulness of the sewage is not greatly increased by allowing solid as well as liquid excreta to enter it.
Sewers are built of glazed stoneware or of impervious brick laid on a bed of concrete to prevent sinking of any part, the parts being most solidly put together with cement. Iron and steel pipes are also used especially when extra strength is required, as when there is some danger of the pipes sinking. For most small streets circular stoneware sewers suffice. Oval brick sewers are more suitable for main streets in which the amount of flow varies greatly. The cross-section of these should be an egg-shaped oval with the small end downwards, as this ensures the most rapid current. Sewers should be laid in as straight a line as possible, and with a fall which will ensure a flow of at least 2½ feet per second. The following rule gives approximately the fall required for smaller sewers and drains:
- A 4-inch pipe requires a fall of 1 in 40.
- A 6-inch pipe requires a fall of 1 in 60.
- A 9-inch pipe requires a fall of 1 in 80.
For further particulars as to the velocity of flow see page [187].
Where a town is very flat, and a proper fall of sewer impossible, Shone’s ejectors are sometimes used to raise the sewage. The sewers are laid in sections, each section falling to a certain point, from which the sewage is raised by the ejector to a higher level and so carried to the next section of sewers. Each section has a separate system of ventilation. The provision of manholes for inspection of an intercepting trap and of ventilation of the house drain near its junction with the sewer has already been considered (page [179]).
As sewers have commonly to carry away the rain-water in addition to the waste matter from houses, their size must be regulated accordingly. The rainfall being very various, the sewers may occasionally become overcharged and flood the basements of houses. During heavy rainfall large quantities of road grit are washed into the sewers, the intercepting gully tanks at the road sides being insufficient to prevent this.
In addition to the above disadvantages associated with discharging storm water into sewers, the sewage owing to its increased bulk is more difficult of disposal, whatever method of disposal be adopted. The size of the sewers and of storm-outfalls into the nearest river or the sea must be regulated so that they are equal to these sudden strains on them; or the Separate system, by which the rain is carried in special conducts to the nearest river, must, in the alternative be adopted. The objections to this plan are that it necessitates a double system of sewerage, and does not allow of the useful scouring effect of rain on sewers. Where it is feasible, and particularly in small country towns, its adoption is advisable. In such cases the old brick drains are used for carrying off rain-water, while new pipe-sewers are employed for carrying the sewage. Such pipe sewers are not liable to become fouled, and on account of the decreased dilution of the sewage can be made smaller than brick-sewers.
Sewers being closed conduits containing sewage, it is highly desirable that the gases resulting from decomposition should be freely diluted. Such gases in unventilated sewers may find their way through intercepting traps into the house drain. The danger from this source has been considerably exaggerated. Ventilation of the sewer is, however, desirable. This has been commonly accomplished by gratings opening at intervals directly into the middle of streets. In narrow streets, the stench from street-grids is occasionally a source of complaint, and may cause malaise and ill-health. Charcoal traps placed below sewer grids to intercept offensive gases have been found to be of little use. The best plan is to do away entirely with surface ventilators, and carry up iron shafts or brick shafts lined with stoneware pipes above the level of all neighbouring houses. The only difficulty in adopting this plan is the difficulty in securing premises to erect such shafts up houses, although no danger attaches to the practice.
Ventilating shafts should be erected at intervals and particularly at the highest points of the sewage system of a town, the upper end of these shafts being remote from the windows of any dwelling-house. When sewers are laid with too steep a gradient, they act as chimneys, the gases mounting to the higher part of the town, and frustrating attempts at ventilation on lower levels. Various attempts have been made to ventilate sewers by artificial means, as by the aspirating effect of street lamps, etc., but these efforts have not been successful, as the effect of the up-current only influences a short length of sewer. The usual method of combined up-shafts and street grids answers fairly well, but when any complaint of smell from street-grids occurs they should be replaced by up-shafts. In Bristol and a few other towns no provision is made for sewer-ventilation, and no ill effects have apparently resulted. There can be no question that the importance of sewer-ventilation has been exaggerated. If the sewer has a sufficient gradient, and is properly laid, and efficiently flushed, so that no offensive deposits occur, the provision of up-shafts at favourable points is all that is necessary. Sewer effluvia have been credited with causing enteric fever, diphtheria, and other diseases. These diseases rarely if ever owe their origin to this cause. The microbes discovered in sewer-air have always been those of the outside atmosphere, and not derived from the sewage. Sewer effluvia might, however, predispose to such diseases, if exposure to them were frequent or protracted, by lowering the powers of resistance of the constitution.
Flushing of Sewers is required at intervals, in order to remove any deposits of grit or other solid matter. Flushing is effected by filling special flushing shafts placed at intervals in the sewers with clean water and then suddenly releasing this.
Whenever there is stagnation, a foul odour is certain to be emitted. The cardinal rule with regard to sewage is to keep it in rapid onward motion, until it has passed the outlet of the sewer. The introduction into a sewer of hot water or waste steam is an occasional cause of nuisance.
The Outfall of a sewer requires to be large and perfectly free in order that the progress of the sewage may not be impeded. When the sewage is discharged into the sea above the low water level, it becomes backed up in the main sewers when the tide is high. The same condition of things has occurred when the outfall is into a river below the water line, or into a tank out of which the sewage has to be pumped. In all these cases the ventilation of the sewers requires to be perfect, and great precautions taken to prevent obstruction of the outflow.
In low-lying sewers where the outfall is impeded, mechanical aids are required to prevent blocking of the sewers. This may be obtained by pumping at the outfall, to enable sewage to escape at all conditions of the tide, or to raise the sewage on to land for irrigation. In the Shone system the sewage is raised to the required height by means of compressed air. In this system the sewage is received into “ejectors.” These are cylindrical reservoirs, in which is a float on a counterpoised lever. When a certain quantity of sewage has entered, a valve opens admitting the compressed air, which forcibly raises the sewage into a higher length of sewer or to the outfall.
[CHAPTER XXVII.]
PROBLEMS AS TO FLOW IN SEWERS.
In order to prevent deposit of solid matter, sewers should be constructed with a sufficient gradient, and of a shape which presents the least surface for friction in proportion to the amount of liquid to be conveyed.
All brick sewers should be egg-shaped, with the narrow end downwards. The egg is formed by two circles touching one another, the diameter of the upper circle being twice that of the lower.
This shape possesses the great advantage that when the depth of the stream is diminished the amount of wetted surface of sewer (wetted perimeter) is diminished in equal proportion, whereas in every other form of sewer it is relatively increased. Thus the friction, which depends on the extent of the wetted perimeter, is kept down to a minimum. Where, as in outfall sewers, the volume of sewage is large, and does not vary greatly in amount, the circular form may be preferable, as it is cheaper and stronger than the egg-shaped sewer. Below 18 inches internal diameter, sewers should be circular in section, and made of stoneware, not brick.
The velocity of flow depends upon (1) the hydraulic mean depth of the stream, and (2) its inclination or fall.
The hydraulic mean depth means the depth of a rectangular channel whose sectional area (and therefore the volume of whose current) equals that of the curved sewer or pipe, concerning which the calculation is made, and whose width equals the entire wetted perimeter of the sewer or pipe. It is thus equal to sectional area ∕ wetted perimeter.
In the case of circular pipes, if we take the diameter to be 1, and assume the pipe to be running full, the sectional area = πr2, where π = 3·1416 and r = half diameter.
The wetted perimeter = 2πr, that is, the circumference of the circle formed by the pipe.
Therefore hydraulic mean depth = h = πr2 ∕ 2πr = ¼;
Similarly when the pipe runs half full—
- πr2 ∕ 2
- h = ——— = ¼
- 2πr ∕ 2
The solution of problems where a smaller arc of a circle is occupied by fluid requires trigonometrical methods, and is not usually needed in practice.
The quantity of fluid discharged in a given time is represented by the product of the sectional area of the stream into its velocity. The greater the hydraulic mean depth the greater is the velocity, if the inclination remains the same.
The velocity of flow is determined by Eytelwein’s formula, which states that the mean velocity per second of a stream of water similar in form to those now under consideration is nine-tenths of a mean proportional between the hydraulic mean depth and the fall in two English miles, if the channel were prolonged so far.
- Thus if f = the fall (in feet) in two miles,
- h = hydraulic mean depth in feet,
- V = mean velocity per second,
- Then V = ·9√(hf),
- or if v = velocity per minute, then
- v = 55√(hf).
It is more convenient to let f = fall in one mile.
Then the formula becomes v = 55√(h × 2f).
How much sewage will a circular drain 3 feet in diameter running half full convey, the fall being 1 in 400?
Here h = (πr2 ∕ 2)/(2πr ∕ 2) = r ∕ 2 = ¾.
- 1 in 400 = x in 5,280 feet (i.e. a mile).
- f = 13·2 in a mile.
- v = 55 × 4·4 = 242 feet per minute.
- = 55√h × 2f.
- S = πr2∕2 = 3·1416 × 9/(4 × 2) = 3·5343.
- v × S = 242 × 3·5343 = 855·8 cubic feet, discharged per minute.
In what way does the size and shape of a sewer affect the velocity of the sewage flowing through it? If a 12-inch pipe sewer, laid at a gradient of 1 in 175, gives a velocity of 3½ feet per second, what would be the velocity if the sewer had a gradient of 1 in 700 (the pipe running half full in each case); and would this latter velocity suffice to keep the sewer clear of deposit?
An elliptical sewer gives greater velocity to flow of small quantities of sewage than a circular one because it exposes a smaller surface for friction.
By formula = v = 55√h × 2f.
- h = ¼ ∴ √h = ½.
- f = 1 in 175 = 30 feet in one mile.
- v = (55 ∕ 2)√60 = 212·85 ft. per min., i.e. slightly over 3½ ft. per sec.
In the second case f = 1 in 700 = 7·56 feet in one mile.
v = (55 ∕ 2)√15·12 = 106·97 feet per minute.
Thus in the first case there is a velocity of 3·55 feet per second, and in the second case of 1·78 feet per second. The latter velocity is quite insufficient to keep the sewer free from deposit, 3 feet per second being the minimum velocity required for that purpose.
Given a sewer 3 feet in diameter, with a fall of 1 in 1,760, what would be the relative discharge if the fall were 1 in 5,280?
In the first case, 1 in 1,760 = 3 in mile.
1 in 5,280 = 1 in mile.
h = r ∕ 2 = ¾.
v = 55√(h × 2f)
= 55√(¾ × 6) = 165/√ = 118.
In second case v = 55√(¾ × 2) = 55√(3 ∕ 2) = 67·9.
Thus the velocity of the two streams would be as 118: 67·9.
Supposing a sewer to have a gradient of 1 in 300, how much would the velocity and discharge be increased by altering the gradient to 1 in 100?
- 1 in 300 = 17·6 in mile.
- 1 in 100 = 52·8 in mile.
As h is not given, we must assume it = ¼;, as it does in circular sewers running full or half full.
- v = 55 √(h x 2f)
- = 55 √(35·2 ∕ 4) = 163 feet per minute.
- v1 = 55 √(104 ∕ 4) = 281 feet per minute.
The increase in discharge may be similarly calculated.
Describe the relation existing in a sewer between gradient, volume, velocity, and size.
By the formula v = 55 √(h. f.)
- Where v = velocity in feet per minute.
- h = hydraulic mean depth = (area of cross section of stream)/(wetted perimeter).
- f = fall in feet in two miles.
In circular sewers h = diameter ∕ 4.
Thus the velocity varies as the square root of h or f.
The volume discharged varies with the value of the factor v × s where s = sectional area of stream.
If h remains constant, with a varying volume of s, then the volume discharged may remain constant. Thus h and v in a circular sewer are the same, whether the sewer runs full or half full. In a V-shaped channel the velocity remains the same whatever the depth of the stream, as its bed and area preserve the same proportions. An egg-shaped sewer approximates the V shape in form.
Similar volumes of sewage have velocities which vary not only with the amount of fall, but the size of the sewer. The friction, as represented by the wetted perimeter, would be much less with sewage half filling a circular sewer, than with the same amount of sewage forming a broad shallow stream on the invert of a large sewer.
[CHAPTER XXVIII.]
THE DISPOSAL OF SEWAGE.
The water-carriage system of sewage is, as the late Dr. Parkes put it, “the cleanest, the readiest, the quickest, and in many cases the most inexpensive method.” But when the sewage is conveyed to the outfall of the sewer, its ultimate disposal is still one of the most difficult problems of the present day. Various plans have been adopted, of which the following are the chief:—
| 1. Discharge into running water. | ||
| 2. Discharge into the sea. | ||
| 3. Separation of solid and liquid parts |  | By settlement. |
| By precipitation. | ||
| 4. Filtration through various artificial media or through land. | ||
| 5. Irrigation. | ||
| 6. Bacterial methods. |
Discharge at once into running water was formerly the favourite plan, as it was certainly the most convenient. The sewage was turned into the nearest water-course, regardless of the facts that this might have to supply the drinking water of people at a lower point, that the mouth of the river tended to become obstructed by sewage mud, that valuable stocks of fish were destroyed, and that the river which had practically become a sewer was a source of annoyance and danger to all on it or near it. The enforcement of the Rivers Pollution Prevention Act of 1876 has not been followed by as great improvement as is desirable.
The sewage entering rivers undergoes considerable purification by subsidence, by oxidation, by the influence of water plants, and still more by the active work of microbes, causing nitrification of nitrogenous matter. The vitality of the typhoid bacillus and of the cholera vibrio when discharged by sewage into a large river is probably not very protracted; but water from such a river would form a very dangerous source of domestic supply.
Discharge into the Sea is resorted to in seaboard towns. The outfall must be carried well below the lowest low-water mark, and to such a point that the incoming tide or wind will not bring the sewage back upon the shore, or on the shore of neighbouring places.
Discharge into an Estuary is only justifiable when the flow of the river is rapid, when the volume of water passing out to sea is very greatly in excess of the volume of sewage, and when there is no possibility of contaminating oyster-layings or beds of mussels or other molluscs.
Objection has been taken to the above method on the ground of waste of manure; but modern sewage is so dilute that its profitable utilization on land still remains a dream.
For a single house or small village, the sewage may be stored in a tank, with an overflow-pipe, out of which the liquid parts escape, and are systematically used to irrigate land, while the solid parts are removed at intervals.
A similar subsidence system has been employed on a larger scale, the liquid parts being irrigated over land, while the solid parts are mixed with street sweepings, and sold as manure.
If the liquid parts in any such system as this are turned into a stream, they are as dangerous as the entire sewage, and the legal prohibition to discharging sewage into streams applies equally to them.
The precipitation of the solid parts of the sewage is rendered much more perfect by the use of chemical agents, and at the same time the dissolved matters are to some extent removed.
Milk of lime has been employed, 6 to 12 grains of quicklime being used for each gallon of sewage. Secondary decomposition is apt to occur in the effluent, causing an offensive smell. Salts of alumina, iron salts, and various combinations of these have also been employed, but with imperfect results.
The London sewage for some years has been treated by adding 2·5 grains of sulphate of iron and 3·7 grains of lime to every gallon of sewage; a reduction of 15 to 20 per cent. in the amount of dissolved organic matter being secured. Polarite or magnetic spongy carbon is used as a filter in certain places, the solid and some of the dissolved sewage being first precipitated by magnetic ferrous carbon (ferrozone). The Amines process consists in applying a mixture of herring brine and lime to the sewage. The sewage is stated to be sterilized by this means. Electrolysis has also been applied to the purification of sewage, as in the Hermite process. In this process sea-water is electrolysed, oxygen-yielding compounds and chlorine being produced.
With regard to all the chemical processes hitherto introduced, the following general statement appears to hold good: they are expensive and not thoroughly efficient.
Sewage sludge is deposited in the tanks in chemical processes and needs separate disposal. At Birmingham the amount of sludge produced daily from the sewage of a thousand persons is nearly a ton. This sludge has been run into rough filter beds and left to dry or carted away for manure, but in its crude state its manurial value is very slight. At Ealing it is mixed with house-refuse and burnt in a destructor. The more modern method is to pass it through a filter-press, thus compressing it into solid cakes which can be sold for manure.
Filtration of the sewage matter has been accomplished in various ways.
Intermittent downward filtration through a considerable depth of soil was stated by the Rivers Pollution Commission to be attended with good results. A porous soil is chosen, and the purified water is received in drains under it. A large part of the organic matter is removed by bacterial agency. Frankland’s experiments shewed that upward filtration through the same media did not purify.
Filtration through artificial media has not been successful with crude sewage. Precipitation by ferrozone followed by filtration through polarite is said to be satisfactory.
Broad Irrigation purifies the sewage efficiently under favourable conditions, the possible exceptions being during rainstorms and during frosty weather. The effluent into the river cannot, however, be regarded as certainly innocuous, though it is better than the effluent from most other processes. Sewage farms are not a commercial success. In such a farm liquid sewage is allowed to flow at intervals over the land, different fields being irrigated in rotation. Immense crops of grass are obtained, but the grass is coarse and rank.
The soil to be irrigated should have a gentle slope, and the effluent be conveyed by subsoil drains about 5 or 6 feet deep into the nearest water-course. The sewage should be delivered in as fresh condition as possible, and should be freed from its coarser portions by settlement or precipitation. The amount of land required is about 1 acre for the sewage of 100 persons. The irrigation must be on the intermittent plan, in order that the soil may undergo aeration; as it is only in this way that the best purifying results can be obtained. The sewage farm should be well drained by deep-laid agricultural drains. The chief purification of the sewage occurs in the superficial layers of the soil. Nitrification ceases at a depth of about 18 inches. The great point, therefore, is to keep the superficial soil in good condition. A similar nitrification occurs in earth-closets (page [195]). No nuisance need arise in connection with a sewage-farm, and the supposition that milk and other products from such a farm are less wholesome than the same products from other farms has proved to be unbased.
Bacterial Methods of Treating Sewage.—Chemical precipitation of sewage is likely to be completely superseded by biological or bacterial methods of sewage disposal. When sewage is treated by filtering through land or by broad irrigation the process is bacterial, bacteria or microbes in the soil converting injurious organic matter into innocuous mineral products. The typical process is one of nitrification. The novelty of recent methods is in utilising bacteria for the whole process of purification, and not only for its final stages. The object is, in fact, not as in chemical processes to arrest, but by confining the sewage in tanks to aid and hasten decomposition or putrefaction. Two kinds of microbes serve in this process; those living in air, known as aerobic, and those living in other gases than air, called anaerobic.
Three biological methods of preliminary treatment of sewage are employed. (1) Mr. Scott Moncrieff passes the sewage slowly upwards through a filter 14 inches thick, consisting of successive layers of flint, coke, and gravel. This is called a “cultivation tank.” The solid sewage becomes liquefied in passing through this medium, the microbes in the filter dissolving the sewage. (2) In the “septic tank method,” introduced by Mr. Cameron at Exeter, a tank is employed which is covered in to exclude light, and to a large extent air. The tank is large enough to hold 24 hours’ flow of sewage. The microbes in the sewage under these conditions multiply rapidly, attack, and liquefy the sewage. As in the first process little or no sludge is left. The ultimate products of the decomposition are water, ammonia, and carbonic acid, and other gases. The effluent from the tank is comparatively clear and inoffensive. (3) Aerobic biological filters are employed, as in Mr. Dibdin’s installation at Sutton, where the filtering material is coke. The sewage slowly passing through the filtering medium becomes liquefied, the solid matter being peptonised. This action is in part at least due to anaerobic microbes. The filtering beds are used intermittently to allow of aeration, and the liquefaction of solid organic particles entangled in the filter probably chiefly occurs at this stage. It is desirable to have small subsidence tanks, for the removal of large suspended matters and of road debris, etc., before the sewage is spread over the filtering beds. The material used in the filter varies. Most commonly coke-breeze has been employed, but coal slack and other material have also been utilised.
After the preliminary treatment above described, the sewage requires to be passed over finer filtering beds, in which aerobic microbes complete the purification by changing the dissolved organic matter into inert inorganic compounds, by the process known as nitrification. The two processes run into one another, to some extent going on together.
Hitherto the Local Government Board have required filtration of sewage through land before any sewage effluent is allowed to pass into a stream. In view of the successful results now obtainable by bacterial processes this requirement will be occasionally waived. It is unsafe to assume, however, that the clear effluent obtained is free from all disease-producing microbes; and drinking water should not be obtained from even a very large river below the point of discharge of such an effluent, without the most efficient sand filtration.
[CHAPTER XXIX.]
CONSERVANCY METHODS.
The refuse to be removed from a house consists of fouled water, which is at least equal in quantity to the water-supply of the house; the excreta of the inhabitants; and “dust,” which contains, besides ashes, considerable kitchen refuse; consisting of both vegetable and animal matters.
In dry methods of removing refuse, the “dust” is often added to the excreta, and the two removed together; or the “dust” may be separately removed. In either case the foul water, and to a large extent the urine, remain to be dealt with, and require special drains for their removal. Thus in large towns, whether dry or wet methods of removing sewage are adopted, drains for the removal of foul-water and rain-water will be required, and it is found that they are practically as foul as if they contained the solid excreta.
The dry methods of removing sewage involve a certain amount of retention about the house; hence the general name of conservancy methods. Of these the most important are—
1. The pail system.
2. The dry-earth system.
3. The midden or privy system.
The Pail System implies in reality the use of a movable cesspool. The pail may be used alone, or may contain ashes and house refuse, or some deodorant. Where the pail is used without any admixture of foreign matter, it should be emptied daily, and care should be taken that the pails for different houses are not exchanged.
In the Goux System the tubs are lined with a composition containing clay and furnished at the lowest part with some absorbent material such as chaff, straw, or hay, which serves to absorb the urine and retard putrefaction. This is, when well managed, somewhat less offensive than the ordinary pail system.
The pails may be supplied with a deodorant, such as sulphate of iron, as at Birmingham, Leeds, etc.; they may be packed with absorbent material, as in the Goux system (Halifax); the ashes and house-refuse may be deposited in the same pail (Edinburgh, Nottingham); or coal ashes may be scattered over the excreta (Manchester, Salford); but all these systems are rapidly being superseded.
Although the pail or tub system is an improvement on the midden system, it is necessarily a cause of considerable nuisance, and its replacement by water-closets should be recommended in towns. In detached country houses it may be retained without nuisance, if the pail or tub is emptied daily, and its contents at once placed in the garden beneath a shallow layer of earth. The pails in large towns are usually collected in specially-constructed closed wagons. In some towns the pail contents have been burnt in a “Destructor” (page [200]) after having been mixed with ashes. In other towns attempts have been made to utilise the excreta, either by selling in their crude condition or after drying and deodorising them by heat. None of these methods repays the cost of collection. Mixing ashes with the excreta diminishes any possible value they may possess as a manure.
The Dry-earth System is an important modification of the pail system. In it dry earth or some other material is added to the excreta, thus converting them immediately into an inodorous mass. Probably the best contrivances for thus deodorising the excreta, as soon as they fall into the receptacle, are Moule’s or Moser’s Earth-Closets.
It is found that 1½ lbs. of dry earth completely deodorise the closet each time it is used. Loamy earth is the most valuable material; a mixture of peat and earth or ashes is very good; sand, gravel, and chalk are practically useless. It is necessary that the earth should be very dry, and that it should be finely sifted. If the earth is damp, decomposition of the excreta speedily occurs. The act of sitting and rising works a hopper which scatters a supply of earth.
Charcoal and sawdust have also been used in connection with Moule’s or Moser’s closet, and with good results. Charcoal has been obtained cheaply for the purpose from street sweepings, and from seaweed, as in Stanford’s closet, in which ½ lb. of charcoal from seaweed is used each time. Mr. Stanford found that while dry clay absorbs only 4 to 5 per cent. of water, dry charcoal prepared from seaweed absorbs 14·7 per cent. The best material, however, is dry earth, but it must be thoroughly dry. The microbes in the earth disintegrate the excreta, converting them into mineral compounds, such as nitrates. Even the paper used disappears. Hence the same earth may be used over again after being stored dry for six weeks. Whether the excreta of an infectious patient are freed from infection by this process is doubtful; if not, the infection might be scattered by means of dust.
The dry earth system is more expensive in use than the pail system, and although applicable to villages and isolated houses, is quite unsuited to large towns, owing to the practical difficulties connected with the procuring and storing of dry earth. The dry earth closet requires frequent attention, in addition to not being so convenient as the pail closet; and there is much less manurial value in the contents of earth closets than in those of pail closets.
The advantages of the earth-closet as compared with the water-closet have been thus summarised by the late Sir Geo. Buchanan. “It is cheaper in the original cost, it is not injured by frost, it is not damaged by improper substances driven down it, and it very greatly diminishes the quantity of water required by each household.” These advantages only accrue when the system is perfectly worked, and do not counterbalance the immense advantage and greater safety of the water-carriage system in towns.
The Privy or Midden System, involving the use of a fixed receptacle, is still prevalent in many towns as well as in innumerable villages. In its worst form, the receptacle consists of a pit with sides of porous materials, allowing percolation of filth in every direction; and in this pit the excreta of whole households are allowed to collect for months. It has been improved by providing a cover to keep out the rain, and thus retard decomposition; still more by providing a drain for the excess of liquid; and by making the sides and bottom of the pit impervious to moisture. The addition of dry ashes to the excreta tends still further to prevent any smell; and the greatest improvement of all consists in raising the receptacle above the ground level, and providing for easy cleaning from the back. The raising of the receptacle involves a diminution in its size, and so prevents the retention of putrefying matters near a house for a long time.
The model Bye-laws of the Local Government Board recommend a capacity for the privy not exceeding 8 cubic-feet, the provision of means for the frequent application of ashes, dust, or dry refuse; they forbid any connection between the privy and the drain; insist on its being at least 6 feet from a dwelling-house (too low a limit); and require a flagged or asphalted floor at least 3 inches above the level of the surrounding ground.
The Nottingham tub-closet forms a link between the pail and midden system. It is really a small movable middenstead, used for receiving excreta, vegetables and ashes.
Even when carefully supervised, middens are almost certain to be productive of evil. They possess two great disadvantages as compared with pails or dry closets. (1) The time between collections of excreta by the scavengers is much longer; and (2) the receptacle for the refuse is part of the structure of the building, and cannot easily be renewed when it has become saturated with excreta.
The use of pails or dry-earth closets is a great improvement on the old middens, but even these compare very unfavourably with water-closets in two respects. (1) The excreta require to be retained about the house for a longer or shorter period, whereas with an efficient water-carriage system, they are at once projected into the sewer. (2) In removing the excreta, the weight of the receptacle has to be added to that of the excreta, while in the water-carriage system, the water serves as the means of transport.
In villages and isolated houses, where no drains are provided for waste water, and the dry system of closets is adopted, the disposal of waste water requires special provision. Very commonly the slops are thrown out of the door, and soak into the ground about the house. They should be carried by means of a waste-pipe into a water-tight cesspool, remote from the house, whence they can be pumped into a field, or carried away by special conduits.
Relative Merits of Dry and Wet Methods. No absolute answer can be given in exclusive favour of either plan. Each is the best under different circumstances; the dry method being chiefly suitable for small villages, and for temporary collections of people, as in camps; and the wet method for towns. The question of value of manure does not enter into the problem, as it seldom repays for carriage.
The objections to the water-carriage system are really due to its not being carried out in an efficient manner. When sewers are properly laid; when they, as well as house-drains, are freely ventilated; when house-drains are efficiently trapped and ventilated near their junction with the sewer; when the drains are efficiently flushed, and the outflow from the sewer is unimpeded, the objections disappear.
These objections are that—(1) the sewers, as underground channels, transfer effluvia and the germs of disease from one place to another; (2) pipes become disjointed owing to being badly laid, and the ground is contaminated; (3) the water supply is in danger of receiving impurities from the sewers. These objections do not hold good in practice. The contamination of water-mains or of wells from sewers implies gross carelessness in the method of laying of sewers or pipes.
The only objections which are of any force, are (4) that water-closets require a large amount of water, and the sewage obtained is greatly diluted, and consequently diminished in value; while (5) the disposal of such an amount of water, in the case of a large inland town, is a problem of the utmost difficulty. Modern engineering enterprise by bringing water from a greater distance, and by aiding the discharge of sewage when necessary by pumping, has overcome these difficulties.
There are many objections to the dry methods of removing excreta. (1) Whatever dry method be adopted, the excreta are retained for some time in or about the house, instead of being immediately removed.
(2) Although the initial outlay in closets and sewers is less than with the water-carriage system, there is the constantly recurring expense of removing the excreta, as well as of cleansing the pails, etc.
(3) In the dry-earth closets, the provision of dry earth or other material involves some expense.
(4) Whatever dry method be adopted, sewers are always required to carry off the foul water, as well as liquid trade products, and a certain proportion at least of the urine. It is impossible to supply sufficient dry earth to absorb all the urine and slops of the population.
Thus, as the Indian Army Sanitary Commission said, speaking of barracks, “to have two systems of cleansing stations—a foul-water system, and a dry-earth system—would simply be paying double where one payment would answer; or, if all the excreta, solid and liquid, are to be carried away, this must be done at a cost ten times greater than that which would be necessary, if all the excreta were removed by drains.”
With some of the dry methods, as where middens or cesspits are drained into the sewers, the sewer-water is more offensive than in towns supplied with water-closets. When a midden or cesspool is drained, the principle of conservation, which distinguishes the dry system from the wet, is practically abandoned; and not only so, but the solid matters still remain to be disposed of, by a tedious process.
(5) The dry systems, involving the retention of excreta about the house, poison the atmosphere. In all towns where the refuse matters are not removed immediately, there is a high mortality, especially among children.
On the other hand, the introduction of the water-carriage system into large towns, with the abolition of midden-heaps and cesspools, has been followed in nearly every case by a diminution in the death-rate, and especially a considerable diminution in that from such diseases as enteric fever. It has furthermore increased the comfort of life, and removed those serious nuisances which are inevitably associated with privies and pail closets, and to a less extent, when care is not exercised, with earth closets.