POSTSCRIPT.

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 obligedHumble Servant,London, 7 Dec. 1773.J. PRIESTLEY.

I cannot help expressing my surprize, that so clear and intelligible an account, of Mr.Smeaton'sair-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 attemptthe 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 ofphlogisticated 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. Thisrevivification of metalsby electricity completes the proof of the electric matter being, or containing phlogiston.

[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 ofphlogisticated 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. Thisrevivification of metalsby electricity completes the proof of the electric matter being, or containing phlogiston.

Since the publication of my former papers I have given more attention to the subject of nitrous air than to any other species of air; and having been pretty fortunate in my inquiries, I shall be able to lay before my reader a more satisfactory account of the curious phenomena occasioned by it, and also of its nature and constitution, than I could do before, though much still remains to be investigated concerning it, and many new objects of inquiry are started.

With a view to discover where the power of nitrous air to diminish common air lay, I evaporated to dryness a quantity of the solution of copper in diluted spirit of nitre; and having procured from it a quantity of agreen precipitate, I threw the focus of a burning-glass upon it, when it was put into a vessel of quicksilver, standing inverted in a bason of quicksilver. In this manner I procured air from it,which appeared to be, in all respects, nitrous air; so that part of the same principle which had escaped during the solution, in the form ofair, had likewise been retained in it, and had not left it in the evaporation of the water.

With great difficulty I also procured a small quantity of the same kind of air from a solution ofironin spirit of nitre, by the same process.

Having, for a different purpose, fired some paper, which had been dipped in a solution of copper in diluted spirit of nitre, in nitrous air, I found there was a considerable addition to the quantity of it; upon which I fired some of the same kind of paper in quicksilver and presently observed that air was produced from it in great plenty. This air, at the first, seemed to have some singular properties, but afterwards I found that it was nothing more than a mixture of nitrous air, from the precipitate of the solution, and of inflammable air, from the paper; but that the former was predominant.

In the mixture of this kind of air with common air, in a trough of water which had been putrid, but which at that time seemed to have recovered its former sweetness (for it was not in the least degree offensive to the smell) a phenomenonsometimes occurred, which for a long time exceedingly delighted and puzzled me; but which was afterwards the means of letting me see much farther into the constitution of nitrous air than I had been able to see before.

When the diminution of the air was nearly completed, the vessel in which the mixture was made began to be filled with the most beautifulwhite fumes, exactly resembling the precipitation of some white substance in a transparent menstruum, or the falling of very fine snow; except that it was much thicker below than above, as indeed is the case in all chemical precipitations. This appearance continued two or three minutes.

At other times I went over the same process, as nearly as possible in the same manner, but without getting this remarkable appearance, and was several times greatly disappointed and chagrined, when I baulked the expectations of my friends, to whom I had described, and meant to have shewn it. This made me give all the attention I possibly could to this experiment, endeavouring to recollect every circumstance, which, though unsuspected at the time, might have contributed to produce this new appearance; and I took a great deal of pains to procure a quantity of this air from the paperabove mentioned for the purpose, which, with a small burning lens, and an uncertain sun, is not a little troublesome. But all that I observed for some time was, that I stood the best chance of succeeding when Iwarmedthe vessel in which the mixture was made, andagitatedthe air during the effervescence.

Finding, at length, that, with the same preparation and attentions, I got the same appearance from a mixture of nitrous and common air in the same trough of water, I concluded that it could not depend upon any thing peculiar to the precipitate of thecoppercontained in thepaperfrom which the air was procured, as I had at first imagined, but upon what was common to it, and pure nitrous air.

Afterwards, having, (with a view to observe whether any crystals would be formed by the union of volatile alkali, and nitrous air, similar to those formed by it and fixed air, as described by Mr. Smeth in hisDissertation on fixed Air) opened the mouth of a phial which was half filled with a volatile alkaline liquor, in a jar of nitrous air (in the manner described p. 11. fig. 4.) I had an appearance which perfectly explained the preceding. All that part of the phial which was above the liquor, and whichcontained common air, was filled with beautifulwhite clouds, as if some fine white powder had been instantly thrown into it, and some of these clouds rose within the jar of nitrous air. This appearance continued about a minute, and then intirely disappeared, the air becoming transparent.

Withdrawing the phial, and exposing it to the common air, it there also became turbid, and soon after the transparency returned. Introducing it again into the nitrous air, the clouds appeared as before. In this manner the white fumes, and transparency, succeeded each other alternately, as often as I chose to repeat the experiment, and would no doubt have continued till the air in the jar had been thoroughly diluted with common air. These appearances were the same with any substance that containedvolatile alkali, fluid or solid.

When, instead of the small phial, I used a large and tall glass jar, this appearance was truly fine and striking, especially when the water in the trough was very transparent. For I had only to put the smallest drop of a volatile alkaline liquor, or the smallest bit of the solid salt, into the jar, and the moment that the mouth of it was opened in a jar of nitrous air, the white clouds above mentioned began tobe formed at the mouth, and presently descended to the bottom, so as to fill the whole, were it ever so large, as with fine snow.

In considering this experiment, I soon perceived that this curious appearance must have been occasioned by the mixture of the nitrous and common air, and therefore that the white clouds must benitrous ammoniac, formed by the acid of the nitrous air, set loose in the decomposition of it by common air, while the phlogiston, which must be another constituent part of nitrous air, entering the common air, is the cause of the diminution it suffers in this process; as it is the cause of a similar diminution, in a variety of other processes.

I would observe, that it is not peculiar to nitrous air to be a test of the fitness of air for respiration. Any other process by which air is diminished and made noxious answers the same purpose. Liver of sulphur for instance, the calcination of metals, or a mixture of iron filings and brimstone will do just the same thing; but the application of them is not so easy, or elegant, and the effect is not so soon perceived. In fact, it isphlogistonthat is the test. If the air be so loaded with this principle that it can take no more, which is seen by its not being diminished in any of the processesabove mentioned, it is noxious; and it is wholesome in proportion to the quantity of phlogiston that it is able to take.

This, I have no doubt, is the true theory of the diminution of common air by nitrous air, the redness of the appearance being nothing more than the usual colour of the fumes, of spirit of nitre, which is now disengaged from the superabundant phlogiston with which it was combined in the nitrous air, and ready to form another union with any thing that is at hand, and capable of it.

With the volatile alkali it forms nitrous ammoniac, water imbibes it like any other acid, even quicksilver is corroded by it; but this action being slow, the redness in this mixture of nitrous and common air continues much longer when the process is made in quicksilver, than when it is made in water, and the diminution, as I have also observed; is by no means so great.

I was confirmed in this opinion when I put a bit of volatile alkaline salt into the jar of quicksilver in which I made the mixture of nitrous and common air. In these circumstances, the vessel being previously filled with the alkaline fumes, the acid immediately joined them, formed the white clouds above mentioned,and the diminution proceeded almost as far as when the process was made in water. That it did not proceed quite so far, I attribute chiefly to the small quantity of calx formed by the slight solution of mercury with the acid fumes not being able to absorb all the fixed air that is precipitated from the common air by the phlogiston.

In part, also, it may be owing to the small quantify of surface in the quicksilver in the vessels that I made use of; in consequence of which the acid fumes could act upon it only in a slow succession, so that part of them, as well as of the fixed air, had an opportunity of forming another union with the diminished air.

This, as I have observed before, was so much the case when the process was made in quicksilver, without any volatile alkali, that when water was admitted to it, after some time, it was not capable of dissolving that union, tho' it would not have taken place if the process had been in water from the first.

In diversifying this experiment, I found that it appeared to very great advantage when I suspended a piece of volatile salt in the common air, previous to the admission of nitrousair to it, inclosing it in a bit of gauze, muslin, or a small net of wire. For, presently after the redness of the mixture begins to go off, the white cloud, like snow, begins to descend from the salt, as if a white powder was shaken out of the bag that contains it. This white cloud presently fills the whole vessel, and the appearance will last about five minutes.

If the salt be not put to the mixture of these two kinds of air till it has perfectly recovered its transparency, the effervescence being completely over, no white cloud will be formed; and, what is rather more remarkable, there is nothing of this appearance when the salt is put into the nitrous air itself. The reason of this must be, that the acid of the nitrous air has a nearer affinity with its phlogiston than with the volatile alkali; though the phlogiston having a nearer affinity with something in the common air, the acid being thereby set loose, will unite with the alkaline vapour, if it be at hand to unite with it.

There is also very little, if any white cloud formed upon holding a piece of the volatile salt within the mouth of a phial containing smoking spirit of nitre. Also when I threw the focus of a burning mirror upon some sal ammoniac in nitrous air, and filled the wholevessel with white fumes which arose from it, they were soon dispersed, and the air was neither diminished nor altered.

I was now fully convinced, that the white cloud which I casually observed, in the first of these experiments, was occasioned by the volatile alkali emitted from the water, which was in a slight degree putrid; and that the warming, and agitation of the vessels, had promoted the emission of the putrid, or alkaline effluvium.

I could not perceive that the diminution of common air by the mixture of nitrous air was sensibly increased by the presence of the volatile alkali. It is possible, however, that, by assisting the water to take up the acid, something less of it may be incorporated with the remaining diminished air than would otherwise have been; but I did not give much attention to this circumstance.

When the phial in which I put the alkaline salts contained any kind of noxious air, the opening of it in nitrous air was not followed by any thing of the appearance above mentioned. This was the case with inflammable air. But when, after agitating the inflammable air in water, I had brought it to a state in which itwas diminished a little by the mixture of nitrous air, the cloudy appearance was in the same proportion; so that this appearance seems to be equally a test of the fitness of air for respiration, with the redness which attends the mixture of it with nitrous air only.

Having generally fastened the small bag which contained the volatile salt to a piece of brass wire in the preceding experiment, I commonly found the end of it corroded, and covered with a blue substance. Also the salt itself, and sometimes the bag was died blue. But finding that this was not the case when I used an iron wire in the same circumstances, but that it becamered, I was satisfied that both the metals had been dissolved by the volatile alkali. At first I had a suspicion that the blue might have come from the copper, out of which the nitrous air had been made. But when the nitrous air was made from iron, the appearances were, in all respects, the same.

I have observed, in the preceding section, that if nitrous air be mixed with common air inlime-water, the surface of the water, where it is contiguous to that mixture, will be covered with an incrustation of lime, shewing that some fixed air had been deposited in the process. It is remarkable, however, as I there also justmentioned, that this is the case when nitrous air alone is put to a vessel of lime-water, after it has been kept in abladder, or only transferred from one vessel to another by a bladder, in the manner described, p. 15. fig. 9.

As I had used the same bladder for transferring various kinds of air, and among the restfixed air, I first imagined that this effect might have been occasioned by a mixture of this fixed air with the nitrous air, and therefore took a fresh bladder; but still the effect was the same. To satisfy myself farther, that the bladder had produced this effect, I put one into a jar of nitrous air, and after it had continued there a day and a night, I found that the nitrous air in this jar, though it was transferred in a glass vessel, made lime-water turbid.

Whether there was any thing in the preparation of these bladders that occasioned their producing this effect, I cannot tell. They were such as I procure from the apothecaries. The thing seems to deserve farther examination, as there seems, in this case, to be the peculiar effect of fixed air from other causes, or else a production of fixed air from materials that have not been supposed to yield it, at least not in circumstances similar to these.

As fixed air united to water dissolves iron, I had the curiosity to try whether fixed air alone would do it; and as nitrous air is of anacidnature, as well as fixed air, I, at the same time, exposed a large surface of iron to both the kinds; first filling two eight ounce phials with nails, and then with quicksilver, and after that displacing the quicksilver in one of the phials by fixed air, and in the other by nitrous air; then inverting them, and leaving them with their mouths immersed in basons of quicksilver.

In these circumstances the two phials stood about two months, when no sensible change at all was produced in the fixed air, or in the iron which had been exposed to it, but a most remarkable, and most unexpected change was made in the nitrous air; and in pursuing the experiment, it was transformed into a species of air, with properties which, at the time of my first publication on this subject, I should not have hesitated to pronounce impossible, viz. air in which a candle burns quite naturally and freely, and which is yet in the highest degree noxious to animals, insomuch that they die the moment they are put into it; whereas, in general, animals live with little sensible inconvenience in air in which candles have burned out. Such, however, is nitrous air, after it has been long exposed to a large surface of iron.

It is not less extraordinary, that a still longer continuance of nitrous air in these circumstances (buthow longdepends upon too many, and too minute circumstances to be ascertained with exactness) makes it not only to admit a candle to burn in it, but enables it to burn with anenlarged flame, by another flame (extending every where to an equal distance from that of the candle, and often plainly distinguishable from it) adhering to it. Sometimes I have perceived the flame of the candle, in these circumstances, to be twice as large as it is naturally, and sometimes not less than five or six times larger; and yet without any thing like anexplosion, as in the firing of the weakest inflammable air.

Nor is the farther progress in the transmutation of nitrous air, in these circumstances, less remarkable. For when it has been brought to the state last mentioned, the agitation of it in fresh water almost instantly takes off that peculiar kind of inflammability, so that it extinguishes a candle, retaining its noxious quality. It also retains its power of diminishing common air in a very great degree.

But this noxious quality, like the noxious quality of all other kinds of air that will bear agitation in water, is taken out of it by this operation, continued about five minutes; inwhich process it suffers a farther and very considerable diminution. It is then itself diminished by fresh nitrous air, and animals live in it very well, about as well as in air in which candles have burned out.

Lastly, One quantity of nitrous air, which had been exposed to iron in quicksilver, from December 18 to January 20, and which happened to stand in water till January 31 (the iron still continuing in the phial) was fired with an explosion, exactly like a weak inflammable air. At the same time another quantity of nitrous air, which had likewise been exposed to iron, standing in quicksilver, till about the same time, and had then stood in water only, without iron, only admitted a candle to burn in it with an enlarged flame, as in the cases above mentioned. But whether the difference I have mentioned in the circumstances of these experiments contributed to this difference in the result, I cannot tell.

Nitrous air treated in the manner above mentioned is diminished about one fourth by standing in quicksilver; and water admitted to it will absorb about half the remainder; but if water only, and no quicksilver, be used from the beginning, the nitrous air will be diminished much faster and farther; so that not more than onefourth, one sixth, or one tenth of the original quantity will remain. But I do not know that there is any difference in the constitution of the air which remains in these two cases.

The water which has imbibed this nitrous air exposed to iron is remarkably green, also the phial containing it becomes deeply, and, I believe, indelibly tinged with green; and if the water be put into another vessel, it presently deposits a considerable quantity of matter, which when dry appears to be the earth or ochre of iron; from which it is evident, that the acid of the nitrous air dissolves the iron; while the phlogiston, being set loose, diminishes nitrous air, as in the process of the iron filings and brimstone.

Upon this hint, instead of usingiron, I introduced a pot ofliver of sulphurinto a jar of nitrous air, and presently found, that what I had before done by means of iron in six weeks, or two months, I could do by liver of sulphur (in consequence, no doubt, of its giving its phlogiston more freely) in less than twenty-four hours, especially when the process was kept warm.

It is remarkable, however, that if the process with liver of sulphur be suffered to proceed,the nitrous air will be diminished much farther. At one time not more than one twentieth of the original quantity remained, and how much farther it right have been diminished, I cannot tell. In this great diminution, it does not admit a candle to burn in it at all; and I generally found this to be the case whenever the diminution had proceeded beyond three fourths of the original quantity[13].

It is something remarkable, that though the diminution of nitrous air by iron filings and brimstone very much resembles the diminution of it by iron only, or by liver of sulphur, yet the iron filings and brimstone never bring it to such a state as that a candle will burn in it; and also that, after this process, it is never capable of diminishing common air. But when it is considered that these properties are destroyed by agitation in water, this difference in the result of processes, in other respects similar, will appear less extraordinary; and they agree in this, that long agitation in water makes both these kinds of nitrous air equally fit for respiration, being equally diminished by fresh nitrous air. It is possible that there would have beena more exact agreement in the result of these processes, if they had been made in equal degrees ofheat; but the process with iron was made in the usual temperature of the atmosphere, and that with liver of sulphur generally near a fire.

It may clearly, I think, be inferred from these experiments, that all the difference between fresh nitrous air, that state of it in which it is partially inflammable, or wholly so, that in which it again extinguishes candles, and that in which it finally becomes fit for respiration, depends upon some difference in themode of the combinationof its acid with phlogiston, or on theproportionbetween these two ingredients in its composition; and it is not improbable but that, by a little more attention to these experiments, the whole mystery of this proportion and combination may be explained.

I must not omit to observe that there was something peculiar in the result of the first experiment which I made with nitrous air exposed to iron; which was that, without any agitation in water, it was diminished by fresh nitrous air, and that a candle burned in it quite naturally. To what this difference was owing I cannot tell. This air, indeed, had been exposed to the iron a week or two longer than inany of the other cases, but I do not imagine that this circumstance could have produced that difference.

When the process is in water with iron, the time in which the diminution is accomplished is exceedingly various; being sometimes completed in a few days, whereas at other times it has required a week or a fortnight. Some kinds of iron also produced this effect much sooner than others, but on what circumstances this difference depends I do not know. What are the varieties in the result of this experiment when it is made in quicksilver I cannot tell, because, on account of its requiring more time, I have not repeated it so often; but I once found that nitrous air was not sensibly changed by having been exposed to iron in quicksilver nine days; whereas in water a very considerable alteration was always made in much less than half that time.

It may just deserve to be mentioned, that nitrous air extremely rarified in an air-pump dissolves iron, and is diminished by it as much as when it is in its native state of condensation.

It is something remarkable, though I never attended to it particularly before I made these last experiments, and it may tend to throw somelight upon them, that when a candle is extinguished, as it never fails to be, in nitrous air, the flame seems to be a little enlarged at its edges, by another bluish flame added to it, just before its extinction.

It is proper to observe in this place, that the electric spark taken in nitrous air diminishes it to one fourth of its original quantity, which is about the quantity of its diminution by iron filings and brimstone, and also by liver of sulphur without heat. The air is also brought by electricity to the same state as it is by iron filings and brimstone, not diminishing common air. If the electric spark be taken in it when it is confined by water tinged with archil, it is presently changed from blue to red, and that to a very great degree.

When the iron nails or wires, which I have used to diminish nitrous air, had done their office, I laid them aside, not suspecting that they could be of any other philosophical use; but after having lain exposed to the open air almost a fortnight; having, for some other purpose, put some of them into a vessel containing common air, standing inverted, and immersed in water, I was surprized to observe that the air in which they were confined was diminished. The diminution proceeded so fast,that the process was completed in about twenty-four hours; for in that time the air was diminished about one fifth, so that it made no effervescence with nitrous air, and was, therefore, no doubt, highly noxious, like air diminished by any other process.

This experiment I have repeated a great number of times, with the same phials, filled with nails or wires that have been suffered to rust in nitrous air, but their power of diminishing common air grows less and less continually. How long it will be before it is quite exhausted I cannot tell. This diminution of air I conclude must arise from the phlogiston, either of the nitrous air or the iron, being some way entangled in the rust, in which the wires were encrusted, and afterwards getting loose from it.

To the experiments upon iron filings and brimstone in nitrous air, I must add, that when a pot full of this mixture had absorbed as much as it could of a jar of nitrous air (which is about three fourths of the whole) I put fresh nitrous air to it, and it continued to absorb, till three or four jars full of it disappeared; but the absorption was exceedingly slow at the last. Also when I drew this pot through the water, and admitted fresh nitrous air to it, it absorbed anotherjar full, and then ceased. But when I scraped off the outer surface of this mixture, which had been so long exposed to the nitrous air, the remainder absorbed more of the air.

When I took the top of the mixture which I had scraped off and threw upon it the focus of a burning-glass, the air in which it was confined was diminished, and became quite noxious; yet when I endeavoured to get air from this matter in a jar full of quicksilver, I was able to procure little or nothing.

It is not a little remarkable that nitrous air diminished by iron filings and brimstone, which is about one fourth, cannot, by agitation in water, be diminished much farther; whereas pure nitrous air may, by the same process, be diminished to one twentieth of its whole bulk, and perhaps much more. This is similar to the effect of the same mixture, and of phlogiston in other cases, on fixed air; for it so far changes its constitution, that it is afterwards incapable of mixing with water. It is similar also to the effect of phlogiston in acid air, which of itself is almost instantly absorbed by water; but by this addition it is first converted into inflammable air, which does not readily mix with water, and which, by long agitationin water, becomes of another constitution, still less miscible with water.

I shall close this section with a few other observations of a miscellaneous nature.

Nitrous air is as much diminished both by iron filings, and also by liver of sulphur, when confined in quicksilver, as when it is exposed to water.

Distilled water tinged blue with the juice of turnsole becomes red on being impregnated with nitrous air; but by being exposed a week or a fortnight to the common atmosphere, in open and shallow vessels, it recovers its blue colour; though, in that time, the greater part of the water will be evaporated. This shews that in time nitrous air escapes from the water with which it is combined, just as fixed air does, though by no means so readily[14].

Having dissolved silver, copper, and iron in equal quantities of spirit of nitre diluted with water, the quantities of nitrous air produced from them were in the following proportion; from iron 8, from copper 6-1/4, from silver 6. Inabout the same proportion also it was necessary to mix water with the spirit of nitre in each case, in order to make it dissolve these metals with equal rapidity, silver requiring the least water, and iron the most.

Phosphorus gave no light in nitrous air, and did not take away from its power of diminishing common air; only when the redness of the mixture went off, the vessel in which it was made was filled with white fumes, as if there had been some volatile alkali in it. The phosphorus itself was unchanged.

There is something remarkable in the effect of nitrous air oninsectsthat are put into it. I observed before that this kind of air is as noxious as any whatever, a mouse dying the moment it is put into it; but frogs and snails (and therefore, probably, other animals whose respiration is not frequent) will bear being exposed to it a considerable time, though they die at length. A frog put into nitrous air struggled much for two or three minutes, and moved now and then for a quarter of an hour, after which it was taken out, but did not recover.Waspsalways died the moment they were put into the nitrous air. I could never observe that they made the least motion in it, nor could they be recovered to life afterwards.This was also the case in general withspiders,flies, andbutterflies. Sometimes, however, spiders would recover after being exposed about a minute to this kind of air.

Considering how fatal nitrous air is to insects, and likewise its great antiseptic power, I conceived that considerable use might be made of it in medicine, especially in the form ofclysters, in which fixed air had been applied with some success; and in order to try whether the bowels of an animal would bear the injection of it, I contrived, with the help of Mr. Hey, to convey a quantity of it up the anus of a dog. But he gave manifest signs of uneasiness, as long as he retained it, which was a considerable time, though in a few hours afterwards he was as lively as ever, and seemed to have suffered nothing from the operation.

Perhaps if nitrous air was diluted either with common air, or fixed air, the bowels might bear it better, and still it might be destructive towormsof all kinds, and be of use to check or correct putrefaction in the intestinal canal, or other parts of the system. I repeat it once more that, being no physician, I run no risk by such proposals as these; and I cannot help flattering myself that, in time, very great medicinal use will be made of the applicationof these different kinds of air to the animal system. Let ingenious physicians attend to this subject, and endeavour to lay hold of the newhandlewhich is now presented them, before it be seized by rash empiricks; who, by an indiscriminate and injudicious application, often ruin the credit of things and processes which might otherwise make an useful addition to themateriaandars medica.

In the first publication of my papers, having experienced the remarkable antiseptic power of nitrous air, I proposed an attempt to preserve anatomical preparations, &c. by means of it; but Mr. Hey, who made the trial, found that, after some months, various animal substances were shriveled, and did not preserve their natural forms in this kind of air.

FOOTNOTES:[13]The result of several of these experiments I had the pleasure of trying in the presence of the celebrated Mr. De Luc of Geneva, when he was upon a visit to Lord Shelburne in Wiltshire.[14]I have not repeated this experiment with that variation of circumstances which an attention to Mr. Bewley's observation will suggest.

[13]The result of several of these experiments I had the pleasure of trying in the presence of the celebrated Mr. De Luc of Geneva, when he was upon a visit to Lord Shelburne in Wiltshire.

[14]I have not repeated this experiment with that variation of circumstances which an attention to Mr. Bewley's observation will suggest.

In my former experiments on this species of air I procured it from spirit of salt, but I have since hit upon a much less expensive method of getting it, by having recourse to the process by which the spirit of salt is itself originally made. For this purpose I fill a small phial with common salt, pour upon it a small quantity of concentrated oil of vitriol, and receive the fumes emitted by it in a vessel previously filled with quicksilver, and standing in a bason of quicksilver, in which it appears in the form of a perfectlytransparent air, being precisely the same thing with that which I had before expelled from the spirit of salt.

This method of procuring acid air is the more convenient, as a phial, once prepared in this manner, will suffice, for common experiments, many weeks; especially if a little more oil of vitriol be occasionally put to it. It only requires a little more heat at the last than at the first. Indeed, at the first, the heat of a person's hand will often be sufficient to make itthrow out the vapour. In warm weather it will even keep smoking many days without the application of any other heat.

On this account, it should be placed where there are no instruments, or any thing of metal, that can be corroded by this acid vapour. It is from dear-bought experience that I give this advice. It may easily be perceived when this phial is throwing out this acid vapour, as it always appears, in the open air, in the form of a light cloud; owing, I suppose, to the acid attracting to itself, and uniting with, the moisture that is in the common atmosphere.

By this process I even made a stronger spirit of salt than can be procured in any other way. For having a little water in the vessel which contains the quicksilver, it imbibes the acid vapour, and at length becomes truly saturated with it. Having, in this manner, impregnated pure water with acid air, I could afterwards expel the same air from it, as from common spirit of salt.

I observed before that this acid vapour, or air, has a strong affinity withphlogiston, so that it decomposes many substances which contain it, and with them forms a permanently inflammable air, no more liable to be imbibedby water than inflammable air procured by any other process, being in fact the very same thing; and that, in some cases, it even dislodges spirit of nitre and oil of vitriol, which in general appear to be stronger acids than itself. I have since observed that, by giving it more time, it will extract phlogiston from substances from which I at first concluded that it was not able to do it, as from dry wood, crusts of bread not burnt, dry flesh, and what is more extraordinary from flints. As there was something peculiar to itself in the process or result of each of these experiments, it may not be improper to mention them distinctly.

Pieces of drycork woodbeing put to the acid air, a small quantity remained not imbibed by water, and was inflammable.

Very dry pieces ofoak, being exposed to this air a day and a night, after imbibing a considerable quantity of it, produced air which was inflammable indeed, but in the slightest degree imaginable. It seemed to be very nearly in the state of common air.

A piece ofivoryimbibed the acid vapour very slowly. In a day and a night, however, about half an ounce measure of permanent air was produced, and it was pretty strongly inflammable.The ivory was not discoloured, but was rendered superficially soft, and clammy, tasting very acid.

Pieces ofbeef, roasted, and made quite dry, but not burnt, absorbed the acid vapour slowly; and when it had continued in this situation all night, from five ounce measures of the air, half a measure was permanent, and pretty strongly inflammable. This experiment succeeded a second time exactly in the same manner; but when I used pieces of white drychicken-fleshthough I allowed the same time, and in other respects the process seemed to go on in the same manner, I could not perceive that any part of the remaining air was inflammable.

Some pieces of a whitish kind offlint, being put into a quantity of acid air, imbibed but a very little of it in a day and a night; but of 2-1/2 ounce measures of it, about half a measure remained unabsorbed by water, and this was strongly inflammable, taking fire just like an equal mixture of inflammable and common air. At another time, however, I could not procure any inflammable air by this means, but to what circumstance these different results were owing I cannot tell.

That inflammable air is produced fromcharcoalin acid air I observed before. I have since found that it may likewise be procured frompit coal, without being charred.

Inflammable air I had also observed to arise from the exposure of spirit of wine, and variousoilysubstances, to the vapour of spirit of salt. I have since made others of a similar nature, and as peculiar circumstances attended some of these experiments, I shall recite them more at large.

Essential oil of mintabsorbed this air pretty fast, and presently became of a deep brown colour. When it was taken out of this air it was of the consistence of treacle, and sunk in water, smelling differently from what it did before; but still the smell of the mint was predominant. Very little or none of the air was fixed, so as to become inflammable; but more time would probably have produced this effect.

Oil of turpentinewas also much thickened, and became of a deep brown colour, by being saturated with acid air.

Etherabsorbed acid air very fast, and became first of a turbid white, and then of a yellowand brown colour. In one night a considerable quantity of permanent air was produced, and it was strongly inflammable.

Having, at one time, fully saturated a quantity of ether with acid air, I admitted bubbles of common air to it, through the quicksilver, by which it was confined, and observed that white fumes were made in it, at the entrance of every bubble, for a considerable time.

At another time, having fully saturated a small quantity of ether with acid air, and having left the phial in which it was contained nearly full of the air, and inverted, it was by some accident overturned; when, instantly, the whole room was filled with a visible fume, like a white cloud, which had very much the smell of ether, but peculiarly offensive. Opening the door and window of the room, this light cloud filled a long passage, and another room. In the mean time the ether was seemingly all vanished, but some time after the surface of the quicksilver in which the experiment had been made was covered with a liquor that tasted very acid; arising, probably, from the moisture in the atmosphere attracted by the acid vapour with which the ether had been impregnated.

This visible cloud I attribute to the union of the moisture in the atmosphere with the compound of the acid air and ether. I have since saturated other quantities of ether with acid air, and found it to be exceedingly volatile, and inflammable. Its exhalation was also visible, but not in so great a degree as in the case above mentioned.

Camphorwas presently reduced into a fluid state by imbibing acid air, but there seemed to be something of a whitish sediment in it. After continuing two days in this situation I admitted water to it; immediately upon which the camphor resumed its former solid state, and, to appearance, was the very same substance that it had been before; but the taste of it was acid, and a very small part of the air was permanent, and slightly inflammable.

The acid air seemed to make no impression upon a piece of Derbyshirespar, of a very dark colour, and which, therefore, seemed to contain a good deal of phlogiston.

As the acid air has so near an affinity with phlogiston, I expected that the fumes ofliver of sulphur, which chemists agree to be phlogistic, would have united with it, so as to form inflammable air; but I was disappointed in that expectation.This substance imbibed half of the acid air to which it was introduced: one fourth of the remainder, after standing one day in quicksilver, was imbibed by water, and what was left extinguished a candle. This experiment, however, seems to prove that acid air and phlogiston may form a permanent kind of air that is not inflammable. Perhaps it may be air in such a state as common air loaded with phlogiston, and from which the fixed air has been precipitated. Or rather, it may be the same thing with inflammable air, that has lost its inflammability by long standing in water. It well deserves a farther examination.

The following experiments are those in which thestronger acidswere made use of, and therefore they may assist us farther to ascertain their affinities with certain substances, with respect to this marine acid in the form of air.

I put a quantity of strong concentratedoil of vitriolto acid air, but it was not at all affected by it in a day and a night. In order to try whether it would not have more power in a more condensed state, I compressed it with an additional atmosphere; but upon taking off this pressure, the air expanded again, and appeared to be not at all diminished. I also put a quantity of strongspirit of nitreto it without anysensible effect. We may conclude, therefore, that the marine acid, in this form of air, is not able to dislodge the other acids from their union with water.

Blue vitriol, which is formed by the union of the vitriolic acid with copper, turned to a dark green the moment that it was put to the acid air, which it absorbed, though slowly. Two pieces, as big as small nuts, absorbed three ounce measures of the air in about half an hour. The green colour was very superficial; for it was easily wiped or washed off.

Green copperasturned to a deeper green upon being put into acid air, which it absorbed slowly.White copperasabsorbed this air very fast, and was dissolved in it.

Sal ammoniac, being the union of spirit of salt with volatile alkali, was no more affected with the acid air than, as I have observed before, common salt was.

I also introduced to the acid air various other substances, without any particular expectation; and it may be worth while to give an account of the results, that the reader may draw from them such conclusions as he shall think reasonable.

Boraxabsorbed acid air about as fast as blue vitriol, but without any thing else that was observable.

Fine whitesugarabsorbed this air slowly, was thoroughly penetrated with it, became of a deep brown colour, and acquired a smell that was peculiarly pungent.

A piece ofquick limebeing put to about twelve or fourteen ounce measures of acid air, and continuing in that situation about two days, there remained one ounce measure of air that was not absorbed by water, and it was very strongly inflammable, as much so as a mixture of half inflammable and half common air. Very particular care was taken that no common air mixed with the acid air in this process. At another time, from about half the quantity of acid air above mentioned, with much less quick-lime, and in the space of one day, I got half an ounce measure of air that was inflammable in a slight degree only. This experiment proves that some part of the phlogiston which escapes from the fuel, in contact with which the lime is burned, adheres to it. But I am very far from thinking that the causticity of quick-lime is at all owing to this circumstance.

I have made a few more experiments on the mixture of acid air withother kinds of air, and think that it may be worth while to mention them, though nothing of consequence, at least nothing but negative conclusions, can be drawn from them.

A quantity of common air saturated with nitrous air was put to a quantity of acid air, and they continued together all night, without any sensible effect. The quantity of both remained the same, and water being admitted to them, it absorbed all the acid air, and left the other just as before.

A mixture of two thirds of air diminished by iron filings and brimstone, and one third acid air, were mixed together, and left to stand four weeks in quicksilver. But when the mixture was examined, water presently imbibed all the acid air, and the diminished air was found to be just the same that it was before. I had imagined that the acid air might have united with the phlogiston with which the diminished air was overcharged, so as to render it wholsome; and I had read an account of the stench arising from putrid bodies being corrected by acid fumes.

The remaining experiments, in which the acid air was principally concerned, are of a miscellaneous nature.

I put a piece of dryiceto a quantity of acid air (as was observed in the section concerningalkalineair) taking it with a forceps, which, as well as the air itself, and the quicksilver by which it had been confined; had been exposed to the open air for an hour, in a pretty strong frost. The moment it touched the air it was dissolved as fast as it would have been by being thrown into a hot fire, and the air was presently imbibed. Putting fresh pieces of ice to that which was dissolved before, they were also dissolved immediately, and the water thus procured did not freeze again, though it was exposed a whole night, in a very intense frost.

Flies and spiders die in acid air, but not so quickly as in nitrous air. This surprized me very much; as I had imagined that nothing could be more speedily fatal to all animal life than this pure acid vapour.

As inflammable air, I have observed, fires at one explosion in the vapour of smoking spirit of nitre, just like an equal mixture of inflammable and common air, I thought it was possible that the fume which naturally rises from commonspirit of salt might have the same effect, but it had not. For this purpose I treated the spirit of salt, as I had before done the smoking spirit of nitre; first filling a phial with it, then inverting it in a vessel containing a quantity of the same acid; and having thrown the inflammable air into it, and thereby driven out all the acid, turning it with its mouth upwards, and immediately applying a candle to it.

Acid air not being so manageable as most of the other kinds of air, I had recourse to the following peculiar method, in order to ascertain itsspecific gravity. Having filled an eight ounce phial with this air, and corked it up, I weighed it very accurately; and then, taking out the cork, I blew very strongly into it with a pair of bellows, that the common air might take place of the acid; and after this I weighed it again, together with the cork, but I could not perceive the least difference in the weight. I conclude, however, from this experiment, that the acid air is heavier than the common air, because the mouth of the phial and the inside of it were evidently moistened by the water which the acid vapour had attracted from the air, which moisture must have added to the weight of the phial.

It will have appeared from my former experiments, that inflammable air consists chiefly, if not wholly, of the union of an acid vapour with phlogiston; that as much of the phlogiston as contributes to make air inflammable is imbibed by the water in which it is agitated; that in this process it soon becomes fit for respiration, and by the continuance of it comes at length to extinguish flame. These observations, and others which I have made upon this kind of air, have been confirmed by my later experiments, especially those in which I have connectedelectrical experimentswith those on air.

The electric spark taken in any kind ofoilproduces inflammable air, as I was led to observe in the following manner. Having found, as will be mentioned hereafter, that ether doubles the quantity of any kind of air to which it is admitted; and being at that time engaged in a course of experiments to ascertain the effect of the electric matter on all the different kinds of air, I had the curiosity to try what it would do withcommon air, thus increasedby means of ether. The very first spark, I observed, increased the quantity of this air very considerably, so that I had very soon six or eight times as much as I began with; and whereas water imbibes all the ether that is put to any kind of air, and leaves it without any visible change, with respect to quantity or quality, this air, on the contrary, was not imbibed by water. It was also very little diminished by the mixture of nitrous air. From whence it was evident, that it had received an addition of some other kind of air, of which it now principally consisted.

In order to determine whether this effect was produced by thewire, or thecementby which the air was confined (as I thought it possible that phlogiston might be discharged from them) I made the experiment in a glass syphon, fig. 19, and by that means I contrived to make the electric spark pass from quicksilver through the air on which I made the experiment, and the effect was the same as before. At one time there happened to be a bubble of common air, without any ether, in one part of the syphon, and another bubble with ether in another part of it; and it was very amusing to observe how the same electric sparks diminished the former of these bubbles, and increased the latter.

It being evident that theetheroccasioned the difference that was observable in these two cases, I next proceeded to take the electric spark in a quantity of ether only, without any air whatever; and observed that every spark produced a small bubble; and though, while the sparks were taken in the ether itself, the generation of air was slow, yet when so much air was collected, that the sparks were obliged to pass through it, in order, to come to the ether and the quicksilver on which it rested, the increase was exceedingly rapid; so that, making the experiment in small tubes, as fig. 16, the quicksilver soon receded beyond the striking distance. This air, by passing through water, was diminished to about one third, and was inflammable.

One quantity of air produced in this manner from ether I suffered to stand two days in water, and after that I transferred it several times through the water, from one vessel to another, and still found that it was very strongly inflammable; so that I have no doubt of its being genuine inflammable air, like that which is produced from metals by acids, or by any other chemical process.

Air produced from ether, mixed both with common and nitrous air, was likewise inflammable;but in the case of the nitrous air, the original quantity bore a very small proportion to the quantity generated.

Concluding that the inflammable matter in this air came from the ether, as being of the class ofoils, I tried other kinds of oil, asoil of olives,oil of turpentine, andessential oil of mint, taking the electric spark in them, without any air to begin with, and found that inflammable air was produced in this manner from them all. The generation of air from oil of turpentine was the quickest, and from the oil of olives the slowest in these three cases.

By the same process I got inflammable air fromspirit of wine, and about as copiously as from the essential oil of mint. This air continued in water a whole night, and when it was transferred into another vessel was strongly inflammable.

In all these cases the inflammable matter might be supposed to arise from the inflammable substances on which the experiments were made. But finding that, by the same process I could get inflammable air from thevolatile spirit of sal ammoniac, I conclude that the phlogiston was in part supplied by the electric matter itself. For though, as I have observed before,the alkaline air which is expelled from the spirit of sal ammoniac be inflammable, it is so in a very slight degree, and can only be perceived to be so when there is a considerable quantity of it.

Endeavouring to procure air from a caustic alkaline liquor, accurately made for me by Mr. Lane, and also from spirit of salt, I found that the electric spark could not be made visible in either of them; so that they must be much more perfect conductors of electricity than water, or other fluid substances. This experiment well deserves to be prosecuted.

I observed before that inflammable air, by standing long in water, and especially by agitation in water, loses its inflammability; and that in the latter case, after passing through a state in which it makes some approach to common air (just admitting a candle to burn in it) it comes to extinguish a candle. I have since made another observation of this kind, which well deserves to be recited. It relates to the inflammable air generated from oak the 27th of July 1771, of which I have made mention before.

This air I have observed to have been but weakly inflammable some months after it was generated, and to have been converted intopretty good or wholesome air by no great degree of agitation in water; but on the 27th of March 1773, I found the remainder of it to be exceedingly good air. A candle burned in it perfectly well, and it was diminished by nitrous air almost as much as common air.

I shall conclude this section with a few miscellaneous observations of no great importance.

Inflammable air is not changed by being made to pass many times through a red-hot iron tube. It is also no more diminished or changed by the fumes of liver of sulphur, or by the electric spark, than I have before observed it to have been by a mixture of iron filings and brimstone. When the electric spark was taken in it, it was confined by a quantity of water tinged blue with the juice of archil, but the colour remained unchanged.

I put twowaspsinto inflammable air, and let them remain there a considerable time, one of them near an hour. They presently ceased to move, and seemed to be quite dead for about half an hour after they were taken into the open air; but then they came to life again, and presently after seemed to be as well as ever they had been.

The additions I have made to my observations onfixed airare neither numerous nor considerable.

The most important of them is a confirmation of my conjecture, that fixed air is capable of forming an union with phlogiston, and thereby becoming a kind of air that is not miscible with water. I had produced this effect before by means of iron filings and brimstone, fermenting in this kind of air; but I have since had a much more decisive and elegant proof of it byelectricity. For after taking a small electric explosion, for about an hour, in the space of an inch of fixed air, confined in a glass tube one tenth of an inch in diameter, fig. 16, I found that when water was admitted to it, only one fourth of the air was imbibed. Probably the whole of it would have been rendered immiscible in water, if the electrical operation had been continued a sufficient time. This air continued several days in water, and was even agitated in water without any farther diminution.It was not, however, common air, for it was not diminished by nitrous air.

By means of iron filings and brimstone I have, since my former experiments, procured a considerable quantity of this kind of air in a method something different from that which I used before. For having placed a pot of this mixture under a receiver, and exhausted it with a pump of Mr. Smeaton's construction, I filled it with fixed air, and then left it plunged under water; so that no common air could have access to it. In this manner, and in about a week, there was, as near as I can recollect, one sixth, or at least one eighth of the whole converted into a permanent air, not imbibed by water.

From this experiment I expected that the same effect would have been produced on fixed air by the fumes ofliver of sulphur; but I was disappointed in that expectation, which surprised me not a little; though this corresponds in some measure, to the effect of phlogiston exhaled from this substance on acid air. Perhaps more time may be requisite for this purpose, for this process was not continued more than a day and a night.

Iron filings and brimstone, I have observed, ferment with great heat in nitrous air, and I have since observed that this process is attended with greater heat in fixed air than in common air.

Though fixed air incorporated with water dissolves iron, fixed air without water has no such power, as I observed before. I imagined that, if it could have dissolved iron, the phlogiston would have united with the air, and have made it immiscible with water, as in the former instances; but after being confined in a phial full of nails from the 15th of December to the 4th of October following, neither the iron nor the air appeared to have been affected by their mutual contact.

Having exposed equal quantities of common and fixed air, in equal and similar cylindrical glass vessels, to equal degrees of heat, by placing them before a fire, and frequently changing their situations, I observed that they were expanded exactly alike, and when removed from the fire they both recovered their former dimensions.

Having had some small suspicion that liver of sulphur, besides emitting phlogiston, mightalso yield some fixed air (which is known to be contained in the salt of tartar from which it is made) I mixed the two ingredients, viz. salt of tartar and brimstone, and putting them into a thin phial, and applying the flame of a candle to it, so as to form the liver of sulphur, I received the air that came from it in this process in a vessel of quicksilver. In this manner I procured a very considerable quantity of fixed air, so that I judged it was all discharged from the tartar. But though it is possible that a small quantity of it may remain in liver of sulphur, when it is made in the most perfect manner, it is not probable that it can be expelled without heat.

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