SECTION II.
Of common Air diminished and made noxious by various processes.
It will have been observed that, in the first publication of my papers, I confined myself chiefly to the narration of the new facts which I had discovered, barely mentioning any hypotheses that occurred to me, and never seeming to lay much stress upon them. The reason why I was so much upon my guard in this respect was, left, in consequence of attaching myself to any hypothesis too soon, the success of my future inquiries might be obstructed. But subsequent experiments having thrown great light upon the preceding ones and having confirmed the few conjectures I then advanced, I may now venture to speak of my hypotheses with a little less diffidence. Still, however, I shall be ready to relinquish any notions I may now entertain, if new facts should hereafter appear not to favour them.
In a great variety of cases I have observed that there is a remarkable diminution of common, or respirable air, in proportion to which it is always rendered unfit for respiration, indisposed to effervesce with nitrous air, and incapable of farther diminution from any other cause. The circumstances which produce this effect I had then observed to be the burning of candles, the respiration of animals, the putrefaction of vegetables or animal substances, the effervescence of iron filings and brimstone, the calcination of metals, the fumes of charcoal, the effluvia of paint made of white-lead and oil, and a mixture of nitrous air.
All these processes, I observed, agree in this one circumstance, and I believe in no other, that the principle which the chemists call phlogiston is set loose; and therefore I concluded that the diminution of the air was, in some way or other, the consequence of the air becoming overcharged with phlogiston,[11] and that water, and growing vegetables, tend to restore this air to a state fit for respiration, by imbibing the superfluous phlogiston. Several experiments which I have since made tend to confirm this supposition.
Common air, I find, is diminished, and rendered noxious, by liver of sulphur, which the chemists say exhales phlogiston, and nothing else. The diminution in this case was one fifth of the whole, and afterwards, as in other similar cases, it made no effervescence with nitrous air.
I found also, after Dr. Hales, that air is diminished by Homberg's pyrophorus.
The same effect is produced by firing gunpowder in air. This I tried by firing the gunpowder in a receiver half exhausted, by which the air was rather more injured than it would have been by candles burning in it.
Air is diminished by a cement made with one half common coarse turpentine and half bees-wax. This was the result of a very casual observation. Having, in an air-pump of Mr. Smeaton's construction, closed that end of the syphon-gage, which is exposed to the outward air, with this cement (which I knew would make it perfectly air-light) instead of sealing it hermetically; I observed that, in a course of time, the quicksilver in that leg kept continually rising, so that the measures I marked upon it were of no use to me; and when I opened that end of the tube, and closed it again, the same consequence always took place. At length, suspecting that this effect must have arisen from the bit of cement diminishing the air to which it was exposed, I covered all the inside of a glass tube with it, and one end of it being quite closed with the cement, I set it perpendicular, with its open end immersed in a bason of quicksilver; and was presently satisfied that my conjecture was well founded: for, in a few days, the quicksilver rose so much within the tube, that the air in the inside appeared to be diminished about one sixth.
To change this air I filled the tube with quicksilver, and pouring it out again, I replaced the tube in its former situation; when the air was diminished again, but not so fast as before. The same lining of cement diminished the air a third time. How long it will retain this power I cannot tell. This cement had been made several months before I made this experiment with it. I must observe, however, that another quantity of this kind of cement, made with a finer and more liquid turpentine, had not the power of diminishing air, except in a very small proportion. Also the common red cement has this property in the same small degree. Common air, however, which had been confined in a glass vessel lined with this cement about a month, was so far injured that a candle would not burn in it. In a longer time it would, I doubt not, have become thoroughly noxious.
Iron that has been suffered to rust in nitrous air diminishes common air very fast, as I shall have occasion to mention when I give a continuation of my experiments on nitrous air.
Lastly, the same effect, I find, is produced by the electric spark, though I had no expectation of this event when I made the experiment.
This experiment, however, and those which I have made in pursuance of it, has fully confirmed another of my conjectures, which relates to the manner in which air is diminished by being overcharged with phlogiston, viz. the phlogiston having a nearer affinity with some of the constituent parts of the air than the fixed air which enters into the composition of it, in consequence of which the fixed air is precipitated.
This I first imagined from perceiving that lime-water became turbid by burning candles over it, p. 44. This was also the case with lime-water confined in air in which an animal substance was putrefying, or in which an animal died, p. 79. and that in which charcoal was burned, p. 81. But, in all these cases, there was a possibility of the fixed air being discharged from the candle, the putrefying substance, the lungs of the animal, or the charcoal. That there is a precipitation of lime when nitrous air is mixed with common air, I had not then observed, but I have since found it to be the case.
That there was no precipitation of lime when brimstone was burned, I observed, p. 45. might be owing to the fixed air and the lime uniting with the vitriolic acid, and making a salt, which was soluble in water; which salt I, indeed, discovered by the evaporation of the water.
I also observed, p. 46, 105. that diminished air being rather lighter than common air is a circumstance in favour of the fixed, or the heavier part of the common air, having been precipitated.
It was upon this idea, together with others similar to it, that I took so much pains to mix fixed air with air diminished by respiration or putrefaction, in order to make it fit for respiration again; and I thought that I had, in general, succeeded to a considerable degree, p. 99, &c. I will add, also, what I did not mention before, that I once endeavoured, but without effect, to preserve mice alive in the same unchanged air, by supplying them with fixed air, when the air in which they were confined began to be injured by their respiration. Without effect, also, I confined for some months, a quantity of quick lime in a given quantity of common air, thinking it might extract the fixed air from it.
The experiments which I made with electricity were solely intended to ascertain what has often been attempted, but, as far as I know, had never been fully accomplished, viz. to change the blue colour of liquors, tinged with vegetable juices, red.
For this purpose I made use of a glass tube, about one tenth of an inch diameter in the inside, as in fig. 16. In one end of this I cemented a piece of wire b, on which I put a brass ball. The lower part from a was filled with water tinged blue, or rather purple, with the juice of turnsole, or archil. This is easily done by an air-pump, the tube being set in a vessel of the tinged water.
Things being thus prepared, I perceived that, after I had taken the electric spark, between the wire b, and the liquor at a, about a minute, the upper part of it began to look red, and in about two minutes it was very manifestly so; and the red part, which was about a quarter of an inch in length, did not readily mix with the rest of the liquor. I observed also, that if the tube lay inclined while I took the sparks, the redness extended twice as far on the lower side as on the upper.
The most important, though the least expected observation, however, was that, in proportion as the liquor became red, it advanced nearer to the wire, so that the space of air in which the sparks were taken was diminished; and at length I found that the diminution was about one fifth of the whole space; after which more electrifying produced no sensible effect.
To determine whether the cause of the change of colour was in the air, or in the electric matter, I expanded the air which had been diminished in the tube by means of an air-pump, till it expelled all the liquor, and admitted fresh blue liquor into its place; but after that, electricity produced no sensible effect, either on the air, or on the liquor; so that it was evident that the electric matter had decomposed the air, and had made it deposite something that was of an acid nature.
In order to determine whether the wire had contributed any thing to this effect, I used wires of different metals, iron, copper, brass, and silver; but the result was the very same with them all.
It was also the same when, by means of a bent glass tube, I made the electric spark without any wire at all, in the following manner. Each leg of the tube, fig. 19. stood in a bason of quicksilver; which, by means of an air-pump, was made to ascend as high as a, a, in each leg, while the space between a and b in each contained the blue liquor, and the space between b and b contained common air. Things being thus disposed, I made the electric spark perform the circuit from one leg to the other, passing from the liquor in one leg of the tube to the liquor in the other leg, through the space of air. The effect was, that the liquor, in both the legs, became red, and the space of air between them was contracted, as before.
Air thus diminished by electricity makes no effervescence with, and is no farther diminished by a mixture of nitrous air; so that it must have been in the highest degree noxious, exactly like air diminished by any other process.
In order to determine what the acid was, which was deposited by the air, and which changed the colour of the blue liquor, I exposed a small quantity of the liquor so changed to the common air, and found that it recovered its blue colour, exactly as water, tinged with the same blue, and impregnated with fixed air, will do. But the following experiment was still more decisive to this purpose. Taking the electric spark upon lime-water, instead of the blue liquor, the lime was precipitated as the air diminished.
From these experiments it pretty clearly follows, that the electric matter either is, or contains phlogiston; since it does the very same thing that phlogiston does. It is also probable, from these experiments, that the sulphureous smell, which is occasioned by electricity, being very different from that of fixed air, the phlogiston in the electric matter itself may contribute to it.
It was now evident that common air diminished by any one of the processes above-mentioned being the same thing, as I have observed, with air diminished by any other of them (since it is not liable to be farther diminished by any other) the loss which it sustains, in all the cases, is, in part, that of the fixed air which entered into its constitution. The fixed air thus precipitated from common air by means of phlogiston unites with lime, if any lime water be ready to receive it, unless there be some other substance at hand, with which it has a greater affinity, as the calces of metals.
If the whole of the diminution of common air was produced by the deposition of fixed air, it would be easy to ascertain the quantity of fixed air that is contained in any given quantity of common air. But it is evident that the whole of the diminution of common air by phlogiston is not owing to the precipitation of fixed air, because a mixture of nitrous air will make a great diminution in all kinds of air that are fit for respiration, even though they never were common air, and though nothing was used in the process for generating them that can be supposed to yield fixed air.
Indeed, it appears, from some of the experiments, that the diminution of some of these kinds of air by nitrous air is so great, and approaches so nearly to the quantity of the diminution of common air by the same process, as to shew that, unless they be very differently affected by phlogiston, very little is to be allowed to the loss of fixed air in the diminution of common air by nitrous air.
The kinds of air on which this experiment was made were inflammable air, nitrous air diminished by iron filings and brimstone, and nitrous air itself; all of which are produced by the solution of metals in acids; and also on common air diminished and made noxious, and therefore deprived of its fixed air by phlogistic processes; and they were restored to a great degree of purity by agitation in water, out of which its own air had been carefully boiled.
To five parts of inflammable air, which had been agitated in water till it was diminished about one half (at which time part of it fired with a weak explosion) I put one part of nitrous air, which diminished it one eighth of the whole. This was done in lime-water, without any precipitation of lime. To compare this with common air, I mixed the same quantity, viz. five parts of this, and one part of nitrous air: when considerable crust of lime was formed upon the surface of the lime water, though the diminution was very little more than in the former process. It is possible, however, that the common air might have taken more nitrous air before it was fully saturated, so as to begin to receive an addition to its bulk.
I agitated in water a quantity of nitrous air phlogisticated with iron filings and brimstone, and found it to be so far restored, that three fourths of an ounce measure of nitrous air being put to two ounce measures of it, made no addition to it.
But the most remarkable of these experiments is that which I made with nitrous air itself which I had no idea of the possibility of reducing to a state fit for respiration by any process whatever, at the time of my former publication on this subject. This air, however, itself, without any previous phlogistication, is purified by agitation in water till it is diminished by fresh nitrous air, and to a very considerable degree.
In a pretty long time I agitated nitrous air in water, supplying it from time to time with more, as the former quantity diminished, till only one eighteenth of the whole quantity remained; in which state it was so wholesome, that a mouse lived in two ounce measures of it more than ten minutes, without shewing any sign of uneasiness; so that I concluded it must have been about as good as air in which candles had burned out. After agitating it again in water, I put one part of fresh nitrous air to five parts of this air, and it was diminished one ninth part. I then agitated it a third time, and putting more nitrous air to it, it was diminished again in the same proportion, and so a fourth time; so that, by continually repeating the process, it would, I doubt not, have been all absorbed. These processes were made in lime-water, without forming any incrustation on the surface of it.
Lastly, I took a quantity of common air, which had been diminished and made noxious by phlogistic processes; and when it had been agitated in water, I found that it was diminished by nitrous air, though not so much as it would have been at the first. After cleansing it a second time, it was diminished again by the same means; and, after that, a third time; and thus there can be no doubt but that, in time, the whole quantity would have disappeared. For I have never found that agitation in water, deprived of its own air, made any addition to a quantity of noxious air; though, a priori, it might have been imagined that, as a saturation with phlogiston diminishes air, the extraction of phlogiston would increase the bulk of it. On the contrary, agitation in water always diminished noxious air a little; indeed, if water be deprived of all its own air, it is impossible to agitate any kind of air in it without some loss. Also, when noxious air has been restored by plants, I never perceived that it gained any addition to its bulk by that means. There was no incrustation of the lime-water in the above-mentioned experiment.
It is not a little remarkable, that those kinds of air which never had been common air, as inflammable air, phlogisticated nitrous air, and nitrous air itself, when rendered wholesome by agitation in water, should be more diminished by fresh nitrous air, than common air which had been made noxious, and restored by the same process; and yet, from the few trials that I have made, I could not help concluding that this is the case.
In this course of experiments I was very near deceiving myself, in consequence of transferring the nitrous air which I made use of in a bladder, in the manner described, p. 15. fig. 9. so as to conclude that there was a precipitation of lime in all the above-mentioned cases, and that even nitrous air itself produced that effect. But after repeated trials, I found that there was no precipitation of lime, except, in the first diminution of common air, when the nitrous air was transferred in a glass vessel.
That the calces of metals contain air, of some kind or other, and that this air contributes to the additional weight of the calces, above that of the metals from which they are made, had been observed by Dr. Hales; and Mr. Hartley had informed me, that when red-lead is boiled in linseed oil, there is a prodigious discharge of air before they incorporate. I had likewise found, that no weight is either gained or lost by the calcination of tin in a close glass vessel; but I purposely deferred making any more experiments on the subject, till we should have some weather in which I could make use of a large burning lens, which I had provided for that and other purposes; but, in the mean time, I was led to the discovery in a different manner.
Having, by the last-recited experiments, been led to consider the electric matter as phlogiston, or something containing phlogiston, I was endeavouring to revivify the calx of lead with it; when I was surprized to perceive a considerable generation of air. It occurred to me, that possibly this effect might arise from the heat communicated to the red-lead by the electric sparks, and therefore I immediately filled a small phial with the red-lead, and heating it with a candle, I presently expelled from it a quantity of air about four or five times the bulk of the lead, the air being received in a vessel of quicksilver. How much more air it would have yielded, I did not try.
Along with the air, a small quantity of water was likewise thrown out; and it immediately occurred to me, that this water and air together must certainly be the cause of the addition of weight in the calx. It still remained to examine what kind of air this was; but admitting water to it, I found that it was imbibed by it, exactly like fixed air, which I therefore immediately concluded it must be[12].
After this, I found that Mr. Lavoisier had completely discovered the same thing, though his apparatus being more complex, and less accurate than mine, he concluded that more of the air discharged from the calces of metals was immiscible with water than I found it to be. It appeared to me that I had never obtained fixed air more pure.
It being now pretty clearly determined, that common air is made to deposit the fixed air which entered into the constitution of it, by means of phlogiston, in all the cases of diminished air, it will follow, that in the precipitation of lime, by breathing into lime-water the fixed air, which incorporates with lime, comes not from the lungs, but from the common air, decomposed by the phlogiston exhaled from them, and discharged, after having been taken in with the aliment, and having performed its function in the animal system.
Thus my conjecture is more confirmed, that the cause of the death of animals in confined air is not owing to the want of any pabulum vitæ, which the air had been supposed to contain, but to the want of a discharge of the phlogistic matter, with which the system was loaded; the air, when once saturated with it, being no sufficient menstruum to take it up.
The instantaneous death of animals put into air so vitiated, I still think is owing to some stimulus, which, by causing immediate, universal and violent convulsions, exhausts the whole of the vis vitæ at once; because, as I have observed, the manner of their death is the very same in all the different kinds of noxious air.
To this section on the subject of diminished, and noxious air, or as it might have been called phlogisticated air, I shall subjoin a letter which I addressed to Sir John Pringle, on the noxious quality of the effluvia of putrid marshes, and which was read at a meeting of the Royal Society, December 16, 1773.
This letter which is printed in the Philosophical Transactions, Vol. 74, p. 90. is immediately followed by another paper, to which I would refer my reader. It was written by Dr. Price, who has so greatly distinguished himself, and done such eminent service to his country, and to mankind, by his calculations relating to the probabilities of human life, and was suggested by his hearing this letter read at the Royal Society. It contains a confirmation of my observations on the noxious effects of stagnant waters by deductions from Mr. Muret's account of the Bills of Mortality for a parish situated among marshes, in the district of Vaud, belonging to the Canton of Bern in Switzerland.
To Sir JOHN PRINGLE, Baronet.
DEAR SIR,
Having pursued my experiments on different kinds of air considerably farther, in several respects, than I had done when I presented the last account of them to the Royal Society; and being encouraged by the favourable notice which the Society has been pleased to take of them, I shall continue my communications on this subject; but, without waiting for the result of a variety of processes, which I have now going on, or of other experiments, which I propose to make, I shall, from time to time, communicate such detached articles, as I shall have given the most attention to, and with respect to which, I shall have been the most successful in my inquiries.
Since the publication of my papers, I have read two treatises, written by Dr. Alexander, of Edinburgh, and am exceedingly pleased with the spirit of philosophical inquiry, which they discover. They appear to me to contain many new, curious, and valuable observations; but one of the conclusions, which he draws from his experiments, I am satisfied, from my own observations, is ill founded, and from the nature of it, must be dangerous. I mean his maintaining, that there is nothing to be apprehended from the neighbourhood of putrid marshes.
I was particularly surprised, to meet with such an opinion as this, in a book inscribed to yourself, who have so clearly explained the great mischief of such a situation, in your excellent treatise on the diseases of the army. On this account, I have thought it not improper, to address to you the following observations and experiments, which I think clearly demonstrate the fallacy of Dr. Alexander's reasoning, indisputably establish your doctrine, and indeed justify the apprehensions of all mankind in this case.
I think it probable enough, that putrid matter, as Dr. Alexander has endeavoured to prove, will preserve other substances from putrefaction; because, being already saturated with the putrid effluvium, it cannot readily take any more; but Dr. Alexander was not aware, that air thus loaded with putrid effluvium is exceedingly noxious when taken into the lungs. I have lately, however, had an opportunity of fully ascertaining how very noxious such air is.
Happening to use at Calne, a much larger trough of water, for the purpose of my experiments, than I had done at Leeds, and not having fresh water so near at hand as I had there, I neglected to change it, till it turned black, and became offensive, but by no means to such a degree, as to deter me from making use of it. In this state of the water, I observed bubbles of air to rise from it, and especially in one place, to which some shelves, that I had in it, directed them; and having set an inverted glass vessel to catch them, in a few days I collected, a considerable quantity of this air, which issued spontaneously from the putrid water; and putting nitrous air to it, I found that no change of colour or diminution ensued, so that it must have been, in the highest degree, noxious. I repeated the same experiment several times afterwards, and always with the same result.
After this, I had the curiosity to try how wholesome air would be affected by this water; when, to my real surprise, I found, that after only one minute's agitation in it, a candle would not burn in it; and, after three or four minutes, it was in the same state with the air, which had issued spontaneously from the same water.
I also found, that common air, confined in a glass vessel, in contact only with this water, and without any agitation, would not admit a candle to burn in it after two days.
These facts certainly demonstrate, that air which either arises from stagnant and putrid water, or which has been for some time in contact with it, must be very unfit for respiration; and yet Dr. Alexander's opinion is rendered so plausible by his experiments, that it is very possible that many persons may be rendered secure, and thoughtless of danger, in a situation in which they must necessarily breathe it. On this account, I have thought it right to make this communication as early as I conveniently could; and as Dr. Alexander appears to be an ingenuous and benevolent man, I doubt not but he will thank me for it.
That air issuing from water, or rather from the soft earth, or mud, at the bottom of pits containing water, is not always unwholesome, I have also had an opportunity of ascertaining. Taking a walk, about two years ago, in the neighbourhood of Wakefield, in Yorkshire, I observed bubbles of air to arise, in remarkably great plenty, from a small pool of water, which, upon inquiry, I was informed had been the place, where some persons had been boring the ground, in order to find coal. These bubbles of air having excited my curiosity, I presently returned, with a bason, and other vessels proper for my purpose, and having stirred the mud with a long stick, I soon got about a pint of this air; and, examining it, found it to be good, common air; at least a candle burned in it very well. I had not then discovered the method of ascertaining the goodness of common air, by a mixture of nitrous air. Previous to the trial, I had suspected that this air would have been found to be inflammable.
I shall conclude this letter with observing, that I have found a remarkable difference in different kinds of water, with respect to their effect on common air agitated in them, and which I am not yet able to account for. If I agitate common air in the water of a deep well, near my house in Calne, which is hard, but clear and sweet, a candle will not burn in it after three minutes. The same is the case with the rain-water, which I get from the roof of my house. But in distilled water, or the water of a spring-well near the house, I must agitate the air about twenty minutes, before it will be so much injured. It may be worth while, to make farther experiments with respect to this property of water.
In consequence of using the rain-water, and the well-water above mentioned, I was very near concluding, contrary to what I have asserted in this treatise, that common air suffers a decomposition by great rarefaction. For when I had collected a considerable quantity of air, which had been rarefied about four hundred times, by an excellent pump made for me by Mr. Smeaton, I always found, that if I filled my receivers with the water above mentioned, though I did it so gradually as to occasion as little agitation as possible, a candle would not burn in the air that remained in them. But when I used distilled water, or fresh spring-water, I undeceived myself.
I think myself honoured by the attention, which, from the first, you have given to my experiments, and am, with the greatest respect,
Dear Sir,
Your most obliged
Humble Servant,
London, 7 Dec. 1773.
J. PRIESTLEY.
POSTSCRIPT.
I cannot help expressing my surprize, that so clear and intelligible an account, of Mr. Smeaton's air-pump, should have been before the public so long, as ever since the publication of the forty-seventh volume of the Philosophical Transactions, printed in 1752, and yet that none of our philosophical instrument-makers should use the construction. The superiority of this pump, to any that are made upon the common plan, is, indeed, prodigious. Few of them will rarefy more than 100 times, and, in a general way, not more than 60 or 70 times; whereas this instrument must be in a poor state indeed, if it does not rarefy 200 or 300 times; and when it is in good order, it will go as far as 1000 times, and sometimes even much farther than that; besides, this instrument is worked with much more ease, than a common air-pump, and either exhausts or condenses at pleasure. In short, to a person engaged in philosophical pursuits, this instrument is an invaluable acquisition. I shall have occasion to recite some experiments, which I could not have made, and which, indeed, I should hardly have dared to attempt, if I had not been possessed of such an air-pump as this. It is much to be wished, that some person of spirit in the trade would attempt the construction of an instrument, which would do great credit to himself, as well as be of eminent service to philosophy.
FOOTNOTES:
[11] On this account, if it was thought convenient to introduce a new term (or rather make a new application of a term already in use among chemists) it might not be amiss to call air that has been diminished, and made noxious by any of the processes above mentioned, or others similar to them, by the common appellation of phlogisticated air; and, if it was necessary, the particular process by which it was phlogisticated might be added; as common air phlogisticated by charcoal, air phlogisticated by the calcination of metals, nitrous air phlogisticated with the liver of sulphur, &c.
[12] Here it becomes me to ask pardon of that excellent philosopher Father Beccaria of Turin, for conjecturing that the phlogiston, with which he revivified metals, did not come from the electric matter itself, but from what was discharged from other pieces of metal with which he made the experiment. See History of Electricity, p. 277, &c. This revivification of metals by electricity completes the proof of the electric matter being, or containing phlogiston.