Experiments and Observations on Different Kinds of Air Part 10

Having satisfied myself with respect to the relation that alkaline air bears to water, I was impatient to find what would be the consequence of mixing this new air with the other kinds with which I was acquainted before, and especially with _acid_ air; having a notion that these two airs, being of opposite natures, might compose a _neutral air_, and perhaps the very same thing with common air. But the moment that these two kinds of air came into contact, a beautiful white cloud was formed, and presently filled the whole vessel in which they were contained. At the same time the quant.i.ty of air began to diminish, and, at length, when the cloud was subsided, there appeared to be formed a solid _while salt_, which was found to be the common _sal ammoniac_, or the marine acid united to the volatile alkali.

The first quant.i.ty that I produced immediately deliquesced, upon being exposed to the common air; but if it was exposed in a very dry and warm place, it almost all evaporated, in a white cloud. I have, however, since, from the same materials, produced the salt above-mentioned in a state not subject to deliquesce or evaporate. This difference, I find, is owing to the proportion of the two kinds of air in the compound. It is only volatile when there is more than a due proportion of either of the const.i.tuent parts. In these cases the smell of the salts is extremely pungent, but very different from one another; being manifestly acid, or alkaline, according to the prevalence of each of these airs respectively.

_Nitrous air_ admitted to alkaline air likewise occasioned a whitish cloud, and part of the air was absorbed; but it presently grew clear again; leaving only a little dimness on the sides of the vessel. This, however, might be a kind of salt, formed by the union of the two kinds of air. There was no other salt formed that I could perceive. Water being admitted to this mixture of nitrous and alkaline air presently absorbed the latter, and left the former possessed of its peculiar properties.

_Fixed air_ admitted to alkaline air formed oblong and slender crystals, which crossed one another, and covered the sides of the vessel in the form of net-work. These crystals must be the same thing with the volatile alkalis which chemists get in a solid form, by the distillation of sal ammoniac with fixed alkaline salts.

_Inflammable air_ admitted to alkaline air exhibited no particular appearance. Water, as in the former experiment, absorbed the alkaline air, and left the inflammable air as it was before. It was remarkable, however, that the water which was admitted to them became whitish, and that this white cloud settled, in the form of a white powder, to the bottom of the vessel.

Alkaline air mixed with _common air_, and standing together several days, first in quicksilver, and then in water (which absorbed the alkaline air) it did not appear that there was any change produced in the common air: at least it was as much diminished by nitrous air as before. The same was the case with a mixture of acid air and common air.

Having mixed air that had been diminished by the fermentation of a mixture of iron filings and brimstone with alkaline air, the water absorbed the latter, but left the former, with respect to the test of nitrous air (and therefore, as I conclude, with respect to all its properties) the same that it was before.

_Spirit of wine_ imbibes alkaline air as readily as water, and seems to be as inflammable afterwards as before.

Alkaline air contracts no union with _olive oil_. They were in contact almost two days, without any diminution of the air. Oil of turpentine, and essential oil of mint, absorbed a very small quant.i.ty of alkaline air, but were not sensibly changed by it.

_Ether_, however, imbibed alkaline air pretty freely; but it was afterwards as inflammable as before, and the colour was not changed. It also evaporated as before, but I did not attend to this last circ.u.mstance very accurately.

_Sulphur_, _nitre_, _common salt_, and _flints_, were put to alkaline air without imbibing any part of it; but _charcoal_, _spunge_, bits of _linen cloth_, and other substances of that nature, seemed to condense this air upon their surfaces; for it began to diminish immediately upon their being put to it; and when they were taken out the alkaline smell they had contracted was so pungent as to be almost intolerable, especially that of the spunge. Perhaps it might be of use to recover persons from swooning. A bit of spunge, about as big as a hazel nut, presently imbibed an ounce measure of alkaline air.

A piece of the insp.i.s.sated juice of _turnsole_ was made very dry and warm, and yet it imbibed a great quant.i.ty of the air; by which it contracted a most pungent smell, but the colour of it was not changed.

_Alum_ undergoes a very remarkable change by the action of alkaline air.

The outward shape and size remain the same, but the internal structure is quite changed, becoming opaque, beautifully white, and, to appearance, in all respects, like alum which had been roasted; and so as not to be at all affected by a degree of heat that would have reduced it to that state by roasting. This effect is produced slowly; and if a piece of alum be taken out of alkaline air before the operation is over, the inside will be transparent, and the outside, to an equal thickness, will be a white crust.

I imagine that the alkaline vapour seizes upon the water that enters into the const.i.tution of crude alum, and which would have been expelled by heat. Roasted alum also imbibes alkaline air, and, like the raw alum that has been exposed to it, acquires a taste that is peculiarly disagreeable.

_Phosphorus_ gave no light in alkaline air, and made no lasting change in its dimensions. It varied, indeed, a little, being sometimes increased and sometimes diminished, but after a day and a night, it was in the same state as at the first. Water absorbed this air just as if nothing had been put to it.

Having put some _spirit of salt_ to alkaline air, the air was presently absorbed, and a little of the white salt above-mentioned was formed. A little remained unabsorbed, and transparent, but upon the admission of common air to it, it instantly became white.

_Oil of vitriol_, also formed a white salt with alkaline air, and this did not rise in white fumes.

Acid air, as I have observed in my former papers, extinguishes a candle.

Alkaline air, on the contrary, I was surprized to find, is slightly inflammable; which, however, seems to confirm the opinion of chemists, that the volatile alkali contains phlogiston.

I dipped a lighted candle into a tall cylindrical vessel, filled with alkaline air, when it went out three or four times successively; but at each time the flame was considerably enlarged, by the addition of another flame, of a pale yellow colour; and at the last time this light flame descended from the top of the vessel to the bottom. At another time, upon presenting a lighted candle to the mouth of the same vessel, filled with the same kind of air, the yellowish flame ascended two inches higher than the flame of the candle. The electric spark taken in alkaline air is red, as it is in common inflammable air.

Though alkaline air be inflammable, it appeared, by the following experiment, to be heavier than the common inflammable air, as well as to contract no union with it. Into a vessel containing a quant.i.ty of inflammable air, I put half as much alkaline air, and then about the same quant.i.ty of acid air. These immediately formed a white cloud, but it did not rise within the s.p.a.ce that was occupied by the inflammable air; so that this latter had kept its place above the alkaline air, and had not mixed with it.

That alkaline air is lighter than acid air is evident from the appearances that attend the mixture, which are indeed very beautiful.

When acid air is introduced into a vessel containing alkaline air, the white cloud which they form appears at the bottom only, and ascends gradually. But when the alkaline air is put to the acid, the whole becomes immediately cloudy, quite to the top of the vessel.

In the last place, I shall observe that alkaline air, as well as acid, dissolves _ice_ as fast as a hot fire can do it. This was tried when both the kinds of air, and every instrument made use of in the experiment, had been exposed to a pretty intense frost several hours. In both cases, also, the water into which the ice was melted dissolved more ice, to a considerable quant.i.ty.

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 circ.u.mstances 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 circ.u.mstance, 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 coa.r.s.e 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_ diminis.h.i.+ng the air to which it was exposed, I covered all the inside of a gla.s.s 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 quant.i.ty of this kind of cement, made with a finer and more liquid turpentine, had not the power of diminis.h.i.+ng 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 gla.s.s 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 const.i.tuent 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 circ.u.mstance 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 quant.i.ty of quick lime in a given quant.i.ty 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 gla.s.s 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 bra.s.s 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 s.p.a.ce 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 s.p.a.ce; 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.