Experiments and Observations on Different Kinds of Air Part 12

This _revivification of metals_ by electricity completes the proof of the electric matter being, or containing phlogiston.

SECTION III.

_Of NITROUS AIR._

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 const.i.tution, 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 quant.i.ty of the solution of copper in diluted spirit of nitre; and having procured from it a quant.i.ty of a _green precipitate_, I threw the focus of a burning-gla.s.s 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 of _air_, 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 quant.i.ty of the same kind of air from a solution of _iron_ in 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 quant.i.ty 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 phenomenon sometimes 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 const.i.tution 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 beautiful _white 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 circ.u.mstance, 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 quant.i.ty of this air from the paper above 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 I _warmed_ the vessel in which the mixture was made, and _agitated_ the 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 the _copper_ contained in the _paper_ from 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 his _Dissertation 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 which contained common air, was filled with beautiful _white 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 contained _volatile alkali_, fluid or solid.

When, instead of the small phial, I used a large and tall gla.s.s 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 to be 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 be _nitrous 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 const.i.tuent 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 is _phlogiston_ that 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 processes above mentioned, it is noxious; and it is wholesome in proportion to the quant.i.ty 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 circ.u.mstances, 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 quant.i.ty 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 nitrous air 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 whole vessel 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 a.s.sisting 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 circ.u.mstance.

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 it was 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 bra.s.s 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 circ.u.mstances, but that it became _red_, 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 in _lime-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 just mentioned, that this is the case when nitrous air alone is put to a vessel of lime-water, after it has been kept in a _bladder_, 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 rest _fixed 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 gla.s.s 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 circ.u.mstances 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 an _acid_ nature, 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 circ.u.mstances 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 p.r.o.nounce 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 circ.u.mstances (but _how long_ depends upon too many, and too minute circ.u.mstances to be ascertained with exactness) makes it not only to admit a candle to burn in it, but enables it to burn with an _enlarged 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 circ.u.mstances, 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 an _explosion_, as in the firing of the weakest inflammable air.

Nor is the farther progress in the trans.m.u.tation of nitrous air, in these circ.u.mstances, 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; in which 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 quant.i.ty 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 quant.i.ty 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 circ.u.mstances 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 one fourth, one sixth, or one tenth of the original quant.i.ty will remain. But I do not know that there is any difference in the const.i.tution 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 quant.i.ty 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 using _iron_, I introduced a pot of _liver of sulphur_ into 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 quant.i.ty 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 quant.i.ty[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 been a more exact agreement in the result of these processes, if they had been made in equal degrees of _heat_; 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 the _mode of the combination_ of its acid with phlogiston, or on the _proportion_ between 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 in any of the other cases, but I do not imagine that this circ.u.mstance 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 circ.u.mstances 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.