Experiments and Observations on Different Kinds of Air Part 15

1. It is something extraordinary that, though ether, as I found, cannot be made to a.s.sume the form of air (the vapour arising from it by heat, being soon condensed by cold, even in quicksilver) yet that a very small quant.i.ty of ether put to any kind of air, except the acid, and alkaline, which it imbibes, almost instantly doubles the apparent quant.i.ty of it; but upon pa.s.sing this air through water, it is presently reduced to its original quant.i.ty again, with little or no change of quality.

I put about the quant.i.ty of half a nut-sh.e.l.l full of ether, inclosed in a gla.s.s tube, through a body of quicksilver, into an ounce measure of common air, confined by quicksilver; upon which it presently began to expand, till it occupied the s.p.a.ce of two ounce measures. It then gradually contracted about one sixth of an ounce measure. Putting more ether to it, it again expanded to two ounce measures; but no more addition of ether would make it expand any farther. Withdrawing the quicksilver, and admitting water to this air, without any agitation, it began to be absorbed; but only about half an ounce measure had disappeared after it had stood an hour in the water. But by once pa.s.sing it through water the air was reduced to its original dimensions. Being tried by a mixture of nitrous air, it appeared not to be so good as fresh air, though the injury it had received was not considerable.

All the phenomena of dilatation and contraction were nearly the same, when, instead of common air, I used nitrous air, fixed air, inflammable air, or any species of phlogisticated common air. The quant.i.ty of each of these kinds of air was nearly doubled while they were kept in quicksilver, but fixed air was not so much increased as the rest, and phlogisticated air less; but after pa.s.sing through the water, they appeared not to have been sensibly changed by the process.

2. Spirit of wine yields no air by means of heat, the vapours being soon condensed by cold, like the vapour of water; yet when, in endeavouring to procure air from it, I made it boil, and catched the air which had rested on the surface of the spirit, and which had been expelled by the heat together with the vapour, in a vessel of quicksilver, and afterwards admitted acid air to it, the vessel was filled with white fumes, as if there had been a mixture of alkaline air along with it. To what this appearance was owing I cannot tell, and indeed I did not examine into it.

3. Having been informed by Dr. Small and Mr. Bolton of Birmingham, that paper dipped in a solution of copper in spirit of nitre would take fire with a moderate heat (a fact which I afterwards found mentioned in the Philosophical Transactions) it occurred to me that this would be very convenient for experiments relating to _ignition_ in different kinds of air; and indeed I found that it was easily fired, either by a burning lens, or the approach of red-hot iron on the outside of the phial in which it was contained, and that any part of it being once fired, the whole was presently reduced to ashes; provided it was previously made thoroughly dry, which, however, it is not very easy to do.

With this preparation, I found that this paper burned freely in all kinds of air, but not in _vacuo_, which is also the case with gunpowder; and, as I have in effect observed before, all the kinds of air in which this paper was burned received an addition to their bulk, which consisted partly of nitrous air, from the nitrous precipitate, and partly of inflammable air, from the paper. As some of the circ.u.mstances attending the ignition of this paper in some of the kinds of air were a little remarkable, I shall just recite them.

Firing this paper in _inflammable_ air, which it did without any ignition of the inflammable air itself, the quant.i.ty increased regularly, till the phial in which the process was made was nearly full; but then it began to decrease, till one third of the whole quant.i.ty disappeared.

A piece of this paper being put to three ounce measures of _acid_ air, a great part of it presently turned yellow, and the air was reduced to one third of the original quant.i.ty, at the same time becoming reddish, exactly like common air in a phial containing smoking spirit of nitre.

After this, by the approach of hot iron, I set fire to the paper; immediately upon which there was a production of air which more than filled the phial. This air appeared, upon examination, to be very little different from pure nitrous air. I repeated this experiment with the same event.

Paper dipped in a solution of mercury, zinc, or iron, in nitrous acid, has, in a small degree, the same property with paper dipped in a solution of copper in the same acid.

4. Gunpowder is also fired in all kinds of air, and, in the quant.i.ty in which I tried it, did not make any sensible change in them, except that the common air in which it was fired would not afterwards admit a candle to burn in it. In order to try this experiment I half exhausted a receiver, and then with a burning-gla.s.s fired the gunpowder which had been previously put into it. By this means I could fire a greater quant.i.ty of gunpowder in a small quant.i.ty of air, and avoid the hazard of blowing up, and breaking my receiver.

I own that I was rather afraid of firing gunpowder in inflammable air, but there was no reason for my fear; for it exploded quite freely in this air, leaving it, in all respects, just as it was before.

In order to make this experiment, and indeed almost all the experiments of firing gunpowder in different kinds of air, I placed the powder upon a convenient stand within my receiver, and having carefully exhausted it by a pump of Mr. Smeaton's construction, I filled the receiver with any kind of air by the apparatus described, p. 19, fig. 14, taking the greatest care that the tubes, &c. which conveyed the air should contain little or no common air. In the experiment with inflammable air a considerable mixture of common air would have been exceedingly hazardous: for, by that a.s.sistance, the inflammable air might have exploded in such a manner, as to have been dangerous to the operator.

Indeed, I believe I should not have ventured to have made the experiment at all with any other pump besides Mr. Smeaton's.

Sometimes, I filled a gla.s.s vessel with quicksilver, and introduced the air to it, when it was inverted in a bason of quicksilver. By this means I intirely avoided any mixture of common air; but then it was not easy to convey the gunpowder into it, in the exact quant.i.ty that was requisite for my purpose. This, however, was the only method by which I could contrive to fire gunpowder in acid or alkaline air, in which it exploded just as it did in nitrous or fixed air.

I burned a considerable quant.i.ty of gunpowder in an exhausted receiver (for it is well known that it will not explode in it) but the air I got from it was very inconsiderable, and in these circ.u.mstances was necessarily mixed with common air. A candle would not burn in it.

SECTION VIII.

_QUERIES, SPECULATIONS, and HINTS._

I begin to be apprehensive lest, after being considered as a _dry experimenter_, I should pa.s.s, with many of my readers, into the opposite character of a _visionary theorist_. A good deal of theory has been interspersed in the course of this work, but, not content with this, I am now entering upon a long section, which contains nothing else.

The conjectures that I have ventured to advance in the body of the work will, I hope, be found to be pretty well supported by facts; but the present section will, I acknowledge, contain many _random thoughts_. I have, however, thrown them together by themselves, that readers of less imagination, and who care not to advance beyond the regions of plain fact, may, if they please, proceed no farther, that their delicacy be not offended.

In extenuation of my offence, let it, however, be considered, that _theory_ and _experiment_ necessarily go hand in hand, every process being intended to ascertain some particular _hypothesis_, which, in fact, is only a conjecture concerning the circ.u.mstances or the cause of some natural operation; consequently that the boldest and most original experimenters are those, who, giving free scope to their imaginations, admit the combination of the most distant ideas; and that though many of these a.s.sociations of ideas, will be wild and chimerical, yet that others will have the chance of giving rise to the greatest and most capital discoveries; such as very cautious, timid, sober, and slow-thinking people would never have come at.

Sir Isaac Newton himself, notwithstanding the great advantage which he derived from a habit of _patient thinking_, indulged bold and excentric thoughts, of which his Queries at the end of his book of Optics are a sufficient evidence. And a quick conception of distant a.n.a.logies, which is the great key to unlock the secret of nature, is by no means incompatible with the spirit of _perseverance_, in investigations calculated to ascertain and pursue those a.n.a.logies.

-- 1. _Speculations concerning the CONSt.i.tUENT PRINCIPLES of the different kinds of AIR, and the CONSt.i.tUTION and ORIGIN of the ATMOSPHERE, &c._

All the kinds of air that appear to me to be essentially distinct from each other are _fixed air_, _acid_ and _alkaline_; for these, and another principle, called _phlogiston_, which I have not been able to exhibit in the form of _air_, and which has never yet been exhibited by itself in _any form_, seem to const.i.tute all the kinds of air that I am acquainted with.

Acid air and phlogiston const.i.tute an air which either extinguishes flame, or is itself inflammable, according, probably, to the quant.i.ty of phlogiston combined in it, or the mode of combination. When it extinguishes flame, it is probably so much charged with the phlogistic matter, as to take no more from a burning candle, which must, therefore, necessarily go out in it. When it is inflammable, it is probably so much charged with phlogiston, that the heat communicated by a burning candle makes it immediately separate itself from the other principle with which it was united, in which separation _heat_ is produced, as in other cases of ignition; the action and reaction, which necessarily attends the separation of the const.i.tuent principles, exciting probably a vibratory motion in them.

Since inflammable, air, by agitation in water, first comes to lose its inflammability, so as to be fit for respiration, and even to admit a candle to burn in it, and then comes to extinguish a candle; it seems probable that water imbibes a great part of this extraordinary charge of phlogiston. And that water _can_ be impregnated with phlogiston, is evident from many of my experiments, especially those in which metals were calcined over it.

Water having this affinity with phlogiston, it is probable that it always contains a considerable portion of it; which phlogiston having a stronger affinity with the acid air, which is perhaps the basis of common air, may by long agitation be communicated to it, so as to leave it over saturated, in consequence of which it will extinguish a candle.

It is possible, however, that inflammable air and air which extinguishes a candle may differ from one another in the _mode_ of the combination of these two const.i.tuent principles, as well as in the proportional quant.i.ty of each; and by agitation in water, or long standing, that mode of combination may change. This we know to be the case with other substances, as with _milk_, from which, by standing only, _cream_ is separated; which by agitation becomes _b.u.t.ter_. Also many substances, being at rest, putrefy, and thereby become quite different from what they were before. If this be the case with inflammable air, the water may imbibe either of the const.i.tuent parts, whenever any proportion of it is spontaneously separated from the rest; and should this ever be that phlogiston, with which air is but slightly overcharged, as by the burning of a candle, it will be recovered to a state in which a candle may burn in it again.

It will be observed, however, that it was only in one instance that I found that strong inflammable air, in its transition to a state in which it extinguishes a candle, would admit a candle to burn in it, and that was very faintly; that then the air was far from being pure, as appeared by the test of nitrous air; and that it was only from a particular quant.i.ty of inflammable air which I got from oak, and which had stood a long time in water, that I ever got air which was as pure as common air.

Indeed, it is much more easy to account for the pa.s.sing of inflammable air into a state in which it extinguishes candles, without any intermediate state, in which it will admit a candle to burn in it, than otherwise. This subject requires and deserves farther investigation. It will also be well worth while to examine what difference the agitation of air in natural or artificial _sea-water_ will occasion.

Since acid air and phlogiston make inflammable air, and since inflammable air is convertible into air fit for respiration, it seems not to be improbable, that these two ingredients are the only essential principles of common air. For this change is produced by agitation in water only, without the addition of any fixed air, though this kind of air, like various other things of a foreign nature, may be combined with it.

Considering also what prodigious quant.i.ties of inflammable air are produced by the burning of small pieces of wood or pit-coal, it may not be improbable but that the _volcanos_, with which there are evident traces of almost the whole surface of the earth having been overspread, may have been the origin of our atmosphere, as well as (according to the opinion of some) of all the solid land.

The superfluous phlogiston of the air, in the state in which it issues from volcanos, may have been imbibed by the waters of the sea, which it is probable originally covered the surface of the earth, though part of it might have united with the acid vapour exhaled from the sea, and by this union have made a considerable and valuable addition to the common ma.s.s of air; and the remainder of this over-charge of phlogiston may have been imbibed by plants as soon as the earth was furnished with them.

That an acid vapour is really exhaled from the sea, by the heat of the sun, seems to be evident from the remarkably different states of the atmosphere, in this respect, in hot and cold climates. In Hudson's bay, and also in Russia, it is said, that metals hardly ever rust, whereas they are remarkably liable to rust in Barbadoes, and other islands between the tropics. See Ellis's Voyage, p. 288. This is also the case in places abounding with salt-springs, as Nantwich in Ches.h.i.+re.

That mild air should consist of parts of so very different a nature as an acid vapour and phlogiston, one of which is so exceedingly corrosive, will not appear surprising to a chemist, who considers the very strong affinity which these two principles are known to have with each other, and the exceedingly different properties which substances composed by them possess. This is exemplified in common _sulphur_, which is as mild as air, and may be taken into the stomach with the utmost safety, though nothing can be more destructive than one of its const.i.tuent parts, separately taken, viz. oil of vitriol. Common air, therefore, notwithstanding its mildness, may be composed of similar principles, and be a real _sulphur_.

That the fixed air which makes part of the atmosphere is not presently imbibed by the waters of the sea, on which it rests, may be owing to the union which this kind of air also appears to be capable of forming with phlogiston. For fixed air is evidently of the nature of an acid; and it appears, in fact, to be capable of being combined with phlogiston, and thereby of const.i.tuting a species of air not liable to be imbibed by water. Phlogiston, however, having a stronger affinity with acid air, which I suppose to be the basis of common air, it is not surprising that, uniting with this, in preference to the fixed air, the latter should be precipitated, whenever a quant.i.ty of common air is made noxious by an over-charge of phlogiston.

The fixed air with which our atmosphere abounds may also be supplied by volcanos, from the vast ma.s.ses of calcareous matter lodged in the earth, together with inflammable air. Also a part of it may be supplied from the fermentation of vegetables upon the surface of it. At present, as fast as it is precipitated and imbibed by one process, it may be set loose by others.

Whether there be, upon, the whole, an increase or a decrease of the general ma.s.s of the atmosphere is not easy to conjecture, but I should imagine that it rather increases. It is true that many processes contribute to a great visible diminution of common air, and that when by other processes it is restored to its former wholesomeness, it is not increased in its dimensions; but volcanos and fires still supply vast quant.i.ties of air, though in a state not yet fit for respiration; and it will have been seen in my experiments, that vegetable and animal substances, dissolved by putrefaction, not only emit phlogiston, but likewise yield a considerable quant.i.ty of permanent elastic air, overloaded indeed with phlogiston, as might be expected, but capable of being purified by those processes in nature by which other noxious air is purified.

That particles are continually detaching themselves from the surfaces of all solid bodies, even the metallic ones, and that these particles const.i.tute the most permanent part of the atmosphere, as Sir Isaac Newton supposed, does not appear to me to be at all probable.

My readers will have observed, that not only is common air liable to be diminished by a mixture of nitrous air, but likewise air originally produced from inflammable air, and even from nitrous air itself, which never contained any fixed air. From this it may be inferred, that the whole of the diminution of common air by phlogiston is not owing to the precipitation of fixed air, but from a real contraction of its dimensions, in consequence of its union with phlogiston. Perhaps an accurate attention to the specific gravity of air procured from these different materials, and in these different states, may determine this matter, and a.s.sist us in investigating the nature of phlogiston.

In what _manner_ air is diminished by phlogiston, independent of the precipitation of any of its const.i.tuent parts, is not easy to conceive; unless air thus diminished be heavier than air not diminished, which I did not find to be the case. It deserves, however, to be tried with more attention. That phlogiston should communicate absolute _levity_ to the bodies with which it is combined, is a supposition that I am not willing to have recourse to, though it would afford an easy solution of this difficulty.

I have likewise observed, that a mouse will live almost as long in inflammable air, when it has been agitated in water, and even before it has been deprived of all its inflammability, as in common air; and yet that in this state it is not, perhaps, so much diminished by nitrous air as common air is. In this case, therefore, the diminution seems to have been occasioned by a contraction of dimensions, and not by a loss of any const.i.tuent part; so that the air is really better, that is, more fit for respiration, than, by the test of nitrous air, it would seem to be.

If this be the case (for it is not easy to judge with accuracy by experiments with small animals) nitrous air will be an accurate test of the goodness of _common air_ only, that is, air containing a considerable proportion of fixed air. But this is the most valuable purpose for which a test of the goodness of air can be wanted. It will still, indeed, serve for a measure of the goodness of air that does not contain fixed air; but, a smaller degree of diminution in this case, must be admitted to be equivalent to a greater diminution in the other.

As I could never, by means of growing vegetables, bring air which had been thoroughly noxious to so pure a state as that a candle would burn in it, it may be suspected that something else besides _vegetation_ is necessary to produce this effect. But it should be considered, that no part of the common atmosphere can ever be in this highly noxious state, or indeed in a state in which a candle will not burn in it; but that even air reduced to this state, either by candles actually burning out in it, or by breathing it, has never failed to be perfectly restored by vegetation, at least so far that candles would burn in it again, and, to all appearance, as well, and as long as ever; so that the growing vegetables, with which the surface of the earth is overspread, may, for any thing that appears to the contrary, be a cause of the purification of the atmosphere sufficiently adequate to the effect.

It may likewise be suspected, that since _agitation in water_ injures pure common air, the agitation of the sea may do more harm than good in this respect. But it requires a much more violent and longer continued agitation of air in water than is ever occasioned by the waves of the sea to do the least sensible injury to it. Indeed a light agitation of air in _putrid water_ injures it very materially; but if the water be sweet, this effect is not produced, except by a long and tedious operation, whereas it requires but a very short time, in comparison, to restore a quant.i.ty of any of the most noxious kinds of air to a very great degree of wholesomeness by the same process.

Dr. Hales found that he could breathe the same air much longer when, in the course of his respiration, it was made to pa.s.s through several folds of cloth dipped in vinegar, in a solution of sea-salt, or in salt of tartar, especially the last. Statical Essays, vol. 1. p. 266. The experiment is valuable, and well deserves to be repeated with a greater variety of circ.u.mstances. I imagine that the effect was produced by those substances, or by the _water_ which they attracted from the air, imbibing the phlogistic matter discharged from the lungs. Perhaps the phlogiston may unite with the watery part of the atmosphere, in preference to any other part of it, and may by that means be more easily transferred to such salts as imbibe moisture.

Sir Isaac Newton defines _flame_ to be _fumus candens_, considering all _smoke_ as being of the same nature, and capable of ignition. But the smoke of common fuel consists of two very different things. That which rises first is mere _water_, loaded with some of the grosser parts of the fuel, and is hardly more capable of becoming red hot than water itself; but the other kind of smoke, which alone is capable of ignition, is properly _inflammable air_, which is also loaded with other heterogeneous matter, so as to appear like a very dense smoke. A lighted candle soon shews them to be essentially different from each other. For one of them instantly takes fire, whereas the other extinguishes a candle.

It is remarkable that gunpowder will take fire, and explode in all kinds of air, without distinction, and that other substances which contain _nitre_ will burn freely in those circ.u.mstances. Now since nothing can burn, unless there be something at hand to receive the phlogiston, which is set loose in the act of ignition, I do not see how this fact can be accounted for, but by supposing that the acid of nitre, being peculiarly formed to unite with phlogiston, immediately receives it. And if the sulphur, which is thereby formed, be instantly decomposed again, as the chemists in general say, thence comes the explosion of gunpowder, which, however, requires the reaction of some inc.u.mbent atmosphere, and without which the materials will only _melt_, and be _dispersed_ without explosion.

Nitrous air seems to consist of the nitrous acid vapour united to phlogiston, together, perhaps, with some small portion of the metallic calx; just as inflammable air consists of the vitriolic or marine acid, and the same phlogistic principle. It should seem, however, that phlogiston has a stronger affinity with the marine acid, if that be the basis of common air; for nitrous air being admitted to common air, it is immediately decomposed; probably by the phlogiston joining with the acid principle of the common air, while the fixed air which it contained is precipitated, and the acid of the nitrous air is absorbed by the water in which the mixture is made, or unites with any volatile alkali that happens to be at hand.