Testing

Testing.—Chemistry is a valuable science, and more fully appreciated every day in its application to home matters; but the average housewife cannot be expected to qualify herself as an analyst. At the same time there are many simple tests for the purity of air, water, and foods that can easily be brought within the range of an ordinarily intelligent woman, and will be found of great service.

Air.—Apart from poisonous gases due to sewers, &c., there is a constituent of air, which, in excess, becomes poisonous also. This is carbonic acid. Wholesome air does not contain more than 5 volumes of carbonic acid in 10,000; as the proportion increases, the quality of the air deteriorates till it becomes actively poisonous. The simplest method of estimating approximately the proportion of carbonic acid present in the air of a room is by shaking up a small quantity of lime water with a certain amount of the air to be tested. The lime water is prepared by shaking slaked lime with distilled water, allowing it to settle, and then carefully drawing off the clear liquid by a siphon, so as not to disturb the sediment. It can be obtained from any druggist, but should be freshly made.

When this lime water is shaken up in a bottle of air containing carbonic acid, the acid combines with the lime, forming an insoluble powder of carbonate of lime, and when this is in sufficient quantity it makes the water turbid, or milky, so that it can be recognised by the eye. By having a series of bottles of various sizes, filling them with the air to be tested, placing in each bottle a large tablespoonful of lime water, and then shaking them vigorously for 3 or 4 minutes, so that all the air in the bottle shall be brought in contact with the lime water, and all the carbonic acid be taken up by the lime, we shall find that in one bottle of the series the turbidity is just perceptible, while in bottles of less size the fluid remains clear, and in those of greater size it is dense.

The following table is given by Dr. Smart as expressing the relation between the size of the bottle in which turbidity occurs and the volume of carbonic acid in the air:—

Size of Bottle in fluid ounces.Carbonic Acid in volumes per 10,000 air.Size of Bottle in fluid ounces.Carbonic Acid in volumes per 10,000 air.
20.635.512
15.645.113
12.554.814
10.564.515
9.173.520
8.082.925
7.292.530
6.5102.040
6.011

If an 8 oz. bottle shows turbidity, the presence of more than 8 volumes per 10,000 is indicated; how much more must be determined by a second experiment. Taking a 6½ oz. bottle, the air is known to contain less than 10 volumes if no precipitate is developed. The carbonic acid can then be stated as constituting from 8 to 10 volumes per 10,000 of the air. But a third experiment with a bottle intermediate in size will correspondingly reduce the limits of uncertainty regarding the carbonic acid figure. There is no test-paper which can be made practically useful as a quantitative test for carbonic acid. (Sanitary Engineer.)

Water.—The tests for water embrace impurities which affect the character of water for drinking, cooking, and washing purposes. Drinking-water should not be too soft, as it provides much of the lime required in building up the bones of the body; the chief evil in drinking-water is the presence of organic ferments. For cooking and washing purposes, water cannot be too soft, and, if used boiled, the presence of organic matters is practically neutralised.

Drinking-water.—In 1871, Dr. Hager published a valuable and simple test for the presence of fermentable poisonous matter. He proposed a tablespoonful of a clear solution of tannin to be added to a tumblerful of water. If no gelatinous turbidity occurs within 5 hours, the water may be considered good. If turbidity occurs within the first hour, the water is unwholesome. If turbidity is displayed within the second hour, the water is not to be recommended. Previously, in 1866, Dr. Hager had recommended for travellers, as a precaution in cholera times, the addition of the following solution (20 drops to 1 pint) to any water they might be about to drink:—Tannic acid, 5 parts; syrup, 4 parts; distilled water, 6 parts; spirit of wine, 12½ parts.

A very simple test for the purity of water is given by Heisch. He observes that good water should be free from colour, and unpleasant odour and flavour, and should quickly afford a good lather with a small proportion of soap. If ½ pint of water be placed in a clean colourless glass-stoppered bottle, a few grains of the best white lump sugar added, and the bottle freely exposed to the daylight in the window of a warm room, the liquid should not become turbid, even after exposure for a week or 10 days. If, while the stopper remains secure, the water becomes turbid, it is open to grave suspicion of sewage contamination; but if it remains clear, it is almost certainly safe for drinking and all domestic purposes.

Hard or Soft Water.—Dissolve a small quantity of good soap in alcohol. Let a few drops fall into a glass of water. If it turns milky, it is hard; if not, it is soft.

Earthy Matters or Alkali.—Take litmus paper dipped in vinegar, and if, on immersion, the paper returns to its true shade, the water does not contain earthy matter or alkali. If a few drops of syrup be added to a water containing an earthy matter, it will turn green.

Carbonic Acid.—Take equal parts of water and clear lime water. If combined or free carbonic acid is present, a precipitate is seen, in which, if a few drops of muriatic acid be added, an effervescence commences.

Magnesia.—Boil the water to 1/20 part of its weight, and then drop a few grains of neutral carbonate of ammonia into a glass of it, and a few drops of phosphate of soda. If magnesia be present, it will fall to the bottom.

Iron.—(a) Boil a little nut-gall, and add to the water. If it turns grey or slate colour, iron is present. (b) Dissolve a little prussiate of potash, and if iron is present, it will turn blue.

Lime.—Into a glass of the water put 2 drops oxalic acid, and blow upon it; if it gets milky, lime is present.

Acid.—Take a piece of litmus paper. If it turns red, there must be acid. If it precipitates on adding lime water, it is carbonic acid. If a blue sugar-paper is turned red, it is a mineral acid, and there would be reason to suspect poisonous metallic salts.

Foods.—Foods are adulterated in three principal ways, viz.:—(1) By replacing a superior article or ingredient by an inferior or cheaper substitute, (2) by adding foreign matters capable of giving an appearance of superiority, (3) by adding water to increase the weight, this being often accompanied by incorporating foreign materials which absorb much water though perhaps otherwise harmless.

Bread.—Pure flour (wheaten) may be replaced by various meals of inferior nutritive value and lower price; if done on a scale to repay the baker, their presence can be at once detected under the microscope. This kind of adulteration is nearly always accompanied by the use of alum, which improves the appearance of bread made from inferior flour, and enables it to hold much more water. The presence of alum can be ascertained easily and rapidly by the logwood test: soak some crumbs of bread for 6 or 7 minutes in an alcoholic solution of logwood containing an excess of carbonate of ammonia, and squeeze it—a more or less deep blue colour is produced. Alum is often used too to hide the employment of damaged flour, containing perhaps only 7 per cent. of gluten instead of 12. The presence of mineral adulterants, which seldom occurs, is proved by burning a sample of the bread and weighing the ash, which should not exceed 7 parts in 1000. Bread is sometimes made of the flour from wheat which has “sprouted” or germinated, and is then inferior. This can only be ascertained by examining the flour: if it has a musty odour and flavour and an acid reaction, the flour has probably been damp for some time; if there is no mustiness but only an acid reaction, sprouted wheat has been employed. The acid reaction is best discovered by stirring some of the flour in water, filtering, and testing with a solution of corallin rendered red with a trace of alkali; if the flour is acid it turns yellow.

Butter.—Cheap butters largely consist of admixtures with other animal fats, especially that known as “butterine” or “bosch.” Analysis of suspected butter could hardly be undertaken by the housewife, but the presence of butterine is probable if the butter breaks in a crumbly manner and loses its colour on being kept melted for a short time at the temperature of boiling water (212° F.).

Milk.—Adulteration chiefly consists in adding water to skim milk and in mixing skim milk with that sold as new. Analysis is possible only to the skilled chemist, but a rough test may be made. The lactoscope devised by Dr. Bond, of Gloucester, is based on the principle of that of Prof. Feser, of Munich, in which the opacity of fresh milk is taken as proportionate to the amount of butter fat. It is useful as providing a ready means of determining with approximate accuracy the richness of milk, and is therefore a rough but sufficient test where adulteration is suspected. As supplied by the Sanitary and Œconomic Association of Gloucester, it consists of a little glass dish with some black horizontal lines on the base, a small measure, and a sort of pipette. The measure is filled with water and emptied into the dish; the pipette is filled with the milk to be tested, which is then dropped into the water, the drops being counted. The mixture of water and milk is stirred, and when the horizontal lines can no longer be seen, say, from a height of 2 ft., the number of drops of milk used are compared with a table supplied, and the approximate amount of butter-fat is read off. This instrument must not be confounded with the various lactometers, which aim at estimating the quality of a milk by its density (specific gravity)—an utterly erroneous proceeding, seeing that a poor milk will often show a higher density than a rich one.

For new milk a capital test is to pour a small quantity into an ordinary glass test-tube graduated from 0 at the top to 100 at the bottom; on allowing the sample to stand, cream will form, and its proportion can be read off at a glance, always allowing 20 hours’ rest. Good new milk should show an average of 11½ per cent. of cream, and will sometimes reach 80 per cent. The quality of skim milk is less easy to estimate by ready means. It should average not less than 1 part of fat in 1000.

As a precaution against possible infection by diseased milk, it is advisable to let all milk be boiled before use, as the boiling temperature is fatal to the disease germs. Such milk, however, is not so digestible or palatable to many people.

Tea.—The present low prices of tea do not afford much scope for profitable adulteration in this country. The chief falsifications to be on the look out for are the artificial colouring of green teas, which, naturally, are hardly distinguishable from black; and the substitution of re-rolled exhausted leaves for genuine fresh leaves. There is also in cheap teas often a considerable proportion of mineral matter, i.e. added dirt. This last can be readily detected by chewing a small quantity of the leaf, when dirt will be felt in the mouth. The presence of exhausted leaves will be manifested by the increased weight of solid matters left on boiling a sample repeatedly and drying the residue. With genuine teas, the average weight of leaves (dried) remaining after exhaustion is 65 per cent.; therefore 1 oz. of tea thoroughly boiled should not give more than ⅔ oz. of exhausted leaves weighed after drying. If the figure is higher, the addition of exhausted leaves to the original tea may be suspected.

Coffee.—Coffee-berries can scarcely be adulterated without easy detection, therefore the best safeguard is to buy the berries and grind them at home. Ground coffee is nearly always adulterated with chicory: in fact a certain proportion is allowed by law, and the chicory is itself often largely mixed with various rubbish which by roasting gives a brown colour to water. The simplest plan for detecting the sophistication of ground coffee is to sprinkle some in a glass of cold water: pure coffee will not colour the water for some time, while chicory and its substitutes will do so immediately.

Cocoa.—This is never sold in the pure state, and no two preparations are alike. The only safeguard is to buy it in packets bearing the name of one of the well-known makers, whose preparations are wholesome and adapted to the demands of the palate.

Pickles.—Pickles and preserved vegetables are often coloured highly by the addition of copper or by boiling the articles in copper vessels. The presence of copper, even in very small proportion, can be easily and rapidly detected by plunging a bright knife-blade into the vessel for a few moments, when, if copper be present, it will coat the knife. Another evil in cheap pickles is the adulteration of the vinegar by means of sulphuric and other acids, generally sulphuric, that being one of the cheapest. A very small addition of sulphuric acid can be detected by pouring a few drops of the vinegar on a small piece of lump sugar and then evaporating the vinegar away on a water bath; the residue will become more or less blackened (carbonised) according to the amount of free mineral acid present. (Hassall.) A water bath can be extemporised out of a china tea-saucer placed on a small saucepan in which water is boiling. A further risk in vinegar containing sulphuric acid is that the acid has been made from pyrites and is contaminated with arsenic.

Pepper.—Pepper-corns may readily be judged by tasting; they cannot easily be replaced by other seeds, but may have been damaged by sea water and retain but little pungency. Ground pepper is often adulterated with flour or starch, whose presence is at once revealed by the microscope. The same may be said of most spices.

Obviously the housewife cannot conduct a critical chemical analysis of any article coming into her household; the most she can do is to detect the presence of inferior or injurious goods. Where analyses are desired, the author will provide them on the terms stated below, on samples being sent to the publishers of this volume, with the necessary instructions:—

1. Chemical and microscopical examination of water, each sample£220
2. Chemical examination of bread, flour, lard, butter, jam, marmalade, sauces, ale, wine, spirits, for adulteration only, each sample110
3. Chemical examination of milk, coffee, tea, spices, pickles, and sweetmeats, for adulteration only, each sample0106