I shall conclude my account of these experiments with observing, that the electric spark is visible in acid air, exactly as it is in common air; and though I kept making this spark a considerable time in a quant.i.ty of it, I did not perceive that any sensible alteration was made in it. A little inflammable air was produced, but not more than might have come from the two iron nails which I made use of in taking the sparks.
FOOTNOTES:
[9] It will be seen, in the second part of this work, that, in some of these processes, I had afterwards more success.
SECTION X.
MISCELLANEOUS OBSERVATIONS.
1. As many of the preceding observations relate to the _vinous_ and _putrefactive_ fermentations, I had the curiosity to endeavour to ascertain in what manner the air would be affected by the _acetous_ fermentation. For this purpose I inclosed a phial full of small beer in a jar standing in water; and observed that, during the first two or three days, there was an increase of the air in the jar, but from that time it gradually decreased, till at length there appeared to be a diminution of about one tenth of the whole quant.i.ty.
During this time the whole surface of it was gradually covered with a sc.u.m, beautifully corrugated. After this there was an increase of the air till there was more than the original quant.i.ty; but this must have been fixed air, not incorporated with the rest of the ma.s.s; for, withdrawing the beer, which I found to be sour, after it had stood 18 or 20 days under the jar, and pa.s.sing the air several times through cold water, the original quant.i.ty was diminished about one ninth. In the remainder a candle would not burn, and a mouse would have died presently.
The smell of this air was exceedingly pungent, but different from that of the putrid effluvium. A mouse lived perfectly well in this air, thus affected with the acetous fermentation; after it had stood several days mixed with four times the quant.i.ty of fixed air.
2. All the kinds of fact.i.tious air on which I have yet made the experiment are highly noxious, except that which is extracted from saltpetre, or alum; but in this even a candle burned just as in common air[10]. In one quant.i.ty which I got from saltpetre a candle not only burned, but the flame was increased, and something was heard like a hissing, similar to the decrepitation of nitre in an open fire. This experiment was made when the air was fresh made, and while it probably contained some particles of nitre, which would have been deposited afterwards. The air was extracted from these substances by heating them in a gun-barrel, which was much corroded and soon spoiled by the experiment. What effect this circ.u.mstance may have had upon the air I have not considered.
November 6, 1772, I had the curiosity to examine the state of a quant.i.ty of this air which had been extracted from saltpetre above a year, and which at first was perfectly wholesome; when, to my very great surprize, I found that it was become, in the highest degree, noxious. It made no effervescence with nitrous air, and a mouse died the moment it was put into it. I had not, however, washed it in rain-water quite ten minutes (and perhaps less time would have been sufficient) when I found, upon trial, that it was restored to its former perfectly wholesome state. It effervesced with nitrous air as much as the best common air ever does; and even a candle burned in it very well, which I had never before observed of any kind of noxious air meliorated by agitation in water.
This series of facts, relating to air extracted from nitre, appear to me to be very extraordinary and important, and, in able hands, may lead to considerable discoveries.
3. There are many substances which impregnate common air in a very remarkable manner, but without making it noxious to animals. Among other things I tried volatile alkaline salts, and camphor; the latter of which I melted with a burning-gla.s.s, in air inclosed in a phial. The mouse, which was put into this air, sneezed and coughed very much, especially after it was taken out; but it presently recovered, and did not appear to have been sensibly injured.
4. Having made several experiments with a mixture of iron filings and brimstone, kneaded to a paste with water, I had the curiosity to try what would be the effect of subst.i.tuting _bra.s.s dust_ in the place of the iron filings. The result was, that when this mixture had stood about three weeks, in a given quant.i.ty of air, it had turned black, but was not increased in bulk. The air also was neither sensibly increased nor decreased, but the nature of it was changed; for it extinguished flame, it would have killed a mouse presently, and was not restored by fixed air, which had been mixed with it several days.
5. I have frequently mentioned my having, at one time, exposed equal quant.i.ties of different kinds of air in jars standing in boiled water.
_Common air_ in this experiment was diminished four sevenths, and the remainder extinguished flame. This experiment demonstrates that water does not absorb air equally, but that it decomposes it, taking one part, and leaving the rest. To be quite sure of this fact, I agitated a quant.i.ty of common air in boiled water, and when I had reduced it from eleven ounce measures to seven, I found that it extinguished a candle, but a mouse lived in it very well. At another time a candle barely went out when the air was diminished one third, and at other times I have found this effect lake place at other very different degrees of diminution.
This difference I attribute to the differences in the state of the water with respect to the air contained in it; for sometimes it had stood longer than at other times before I made use of it. I also used distilled-water, rain-water, and water out of which the air had been pumped, promiscuously with rain water. I even doubt, not but that, in a certain state of the water, there might be no sensible difference in the bulk of the agitated air, and yet at the end of the process it would extinguish a candle, air being supplied from the water in the place of that part of the common air which had been absorbed.
It is certainly a little extraordinary that the very same process should so far mend putrid air, as to reduce it to the standard of air in which candles have burned out; and yet that it should so far injure common and wholesome air as to reduce it to about the same standard: but so the fact certainly is. If air extinguish flame in consequence of its being previously saturated with phlogiston, it must, in this case, have been transferred from the water to the air, and it is by no means inconsistent with this hypothesis to suppose, that, if the air be over saturated with phlogiston, the water will imbibe it, till it be reduced to the same proportion that agitation in water would have communicated to it.
To a quant.i.ty of common air, thus diminished by agitation in water, till it extinguished a candle, I put a plant, but it did not so far restore it as that a candle would burn in it again; which to me appeared not a little extraordinary, as it did not seem to be in a worse state than air in which candles had burned out, and which had never failed to be restored by the same means.
I had no better success with a quant.i.ty of permanent air which I had collected from my pump-water. Indeed these experiments were begun before I was acquainted with that property of nitrous air, which makes it so accurate a measure of the goodness of other kinds of air; and it might perhaps be rather too late in the year when I made the experiments.
Having neglected these two jars of air, the plants died and putrefied in both of them; and then I found the air in them both to be highly noxious, and to make no effervescence with nitrous air.
I found that a pint of my pump-water contained about one fourth of an ounce measure of air, one half of which was afterwards absorbed by standing in fresh pump-water. A candle would not burn in this air, but a mouse lived in it very well. Upon the whole, it seemed to be in about the same state as air in which a candle had burned out.
6. I once imagined that, by mere _stagnation_, air might become unfit for respiration, or at least the burning of candles; but if this be the case, and the change be produced gradually, it must require a long time for the purpose. For on the 22d of September 1772, I examined a quant.i.ty of common air, which had been kept in a phial, without agitation, from May 1771, and found it to be in no respect worse than fresh air, even by the test of the nitrous air.
7. The crystallization of nitre makes no sensible alteration in the air in which the process is made. For this purpose I dissolved as much nitre as a quant.i.ty of hot water would contain, and let it cool under a receiver, standing in water.
8. November 6, 1772, a quant.i.ty of inflammable air, which, by long keeping, had come to extinguish flame, I observed to smell very much like common air in which a mixture of iron filings and brimstone had stood. It was not, however, quite so strong, but it was equally noxious.
9. Bis.m.u.th and nickel are dissolved in the marine acid with the application of a considerable degree of heat; but little or no air is got from either of them; but, what I thought a little remarkable, both of them smelled very much like Harrowgate water, or liver of sulphur.
This smell I have met with several times in the course of my experiments, and in processes very different from one another.
FOOTNOTES:
[10] Experiments, of which an account will be given in the second part of this work, make it probable, that though a candle burned even _more than well_ in this air, an animal would not have lived in it. At the time of this first publication, however, I had no idea of this being possible in nature.
PART II.
_Experiments and Observations made in the Year 1773, and the Beginning of 1774._
SECTION I.
_Observations on ALKALINE AIR._
After I had made the discovery of the _marine acid air_, which the vapour of spirit of salt may properly enough be called, and had made those experiments upon it, of which I have given an account in the former part of this work, and others which I propose to recite in this part; it occurred to me, that, by a process similar to that by which this _acid_ air is expelled from the spirit of salt, an _alkaline_ air might be expelled from substances containing volatile alkali.
Accordingly I procured some volatile spirit of sal ammoniac, and having put it into a thin phial, and heated it with the flame of a candle, I presently found that a great quant.i.ty of vapour was discharged from it; and being received in a vessel of quicksilver, standing in a bason of quicksilver, it continued in the form of a transparent and permanent air, not at all condensed by cold; so that I had the same opportunity of making experiments upon it, as I had before on the acid air, being in the same favourable circ.u.mstances.
With the same ease I also procured this air from _spirit of hartshorn_, and _sal volatile_ either in a fluid or solid form, i. e. from those volatile alkaline salts which are produced by the distillation of sal ammoniac with fixed alkalis. But in this case I soon found that the alkaline air I procured was not pure; for the fixed air, which entered into the composition of my materials, was expelled along with it. Also, uniting again with the alkaline air, in the gla.s.s tube through which they were conveyed, they stopped it up, and were often the means of bursting my vessels.
While these experiments were new to me, I imagined that I was able to procure this air with peculiar advantage and in the greatest abundance, either from the salts in a dry state, when they were just covered with water, or in a perfectly fluid state; for, upon applying a candle to the phials in which they were contained, there was a most astonishing production of air; but having examined it, I found it to be chiefly fixed air, especially after the first or second produce from the same materials; and removing my apparatus to a trough of water and using the water instead of quicksilver, I found that it was not presently absorbed by it.
This, however, appears to be an easy and elegant method of procuring fixed air, from a small quant.i.ty of materials, though there must be a mixture of alkaline air along with it; as it is by means of its combination with this principle only, that it is possible, that so much fixed air should be retained in any liquid. Water, at least, we know, cannot be made to contain much more than its own bulk of fixed air.
After this disappointment, I confined myself to the use of that volatile spirit of sal ammoniac which is procured by a distillation with slaked lime, which contains no fixed air; and which seems, in a general state, to contain about as much alkaline air, as an equal quant.i.ty of spirit of salt contains of the acid air.
Wanting, however, to procure this air in greater quant.i.ties, and this method being rather expensive, it occurred to me, that alkaline air might, probably, be procured, with the most ease and convenience, from the original materials, mixed in the same proportions that chemists had found by experience to answer the best for the production of the volatile spirit of sal ammoniac. Accordingly I mixed one fourth of pounded sal ammoniac, with three fourths of slaked lime; and filling a phial with the mixture, I presently found it completely answered my purpose. The heat of a candle expelled from this mixture a prodigious quant.i.ty of alkaline air; and the same materials (as much as filled an ounce phial) would serve me a considerable time, without changing; especially when, instead of a gla.s.s phial, I made use of a small iron tube, which I find much more convenient for the purpose.
As water soon begins to rise in this process, it is necessary, if the air is intended to be conveyed perfectly _dry_ into the vessel of quicksilver, to have a small vessel in which this water (which is the common volatile spirit of sal ammoniac) may be received. This small vessel must be interposed between the vessel which contains the materials for the generation of the air, and that in which it is to be received, as _d_ fig. 8.
This _alkaline_ air being perfectly a.n.a.logous to the _acid_ air, I was naturally led to investigate the properties of it in the same manner, and nearly in the same order. From this a.n.a.logy I concluded, as I presently found to be the fact, that this alkaline air would be readily imbibed by water, and, by its union with it, would form a volatile spirit of sal ammoniac. And as the water, when admitted to the air in this manner, confined by quicksilver, has an opportunity of fully saturating itself with the alkaline vapour, it is made prodigiously stronger than any volatile spirit of sal ammoniac that I have ever seen; and I believe stronger than it can be made in the common way.
In order to ascertain what addition, with respect to quant.i.ty and weight, water would acquire by being saturated with alkaline air, I put 1-1/4 grains of rain-water into a small gla.s.s tube, closed at one end with cement, and open at the other, the column of water measuring 7/10 of an inch; and having introduced it through the quicksilver into a vessel containing alkaline air, observed that it absorbed 7/8 of an ounce measure of the _air_, and had then gained about half a grain in weight, and was increased to 8-1/2 tenths of an inch in length. I did not make a second experiment of this kind, and therefore will not answer for the exactness of these proportions in future trials. What I did sufficiently answered my purpose, in a general view of the subject.
When I had, at one time, saturated a quant.i.ty of distilled water with alkaline air, so that a good deal of the air remained unabsorbed on the surface of the water, I observed that, as I continued to throw up more air, a considerable proportion of it was imbibed, but not the whole; and when I had let the apparatus stand a day, much more of the air that lay on the surface was imbibed. And after the water would imbibe no more of the _old_ air, it imbibed _new_. This shews that water requires a considerable time to saturate itself with this kind of air, and that part of it more readily unites with water than the rest.
The same is also, probably, the case with all the kinds of air with which water can be impregnated. Mr. Cavendish made this observation with respect to fixed air, and I repeated the whole process above-mentioned with acid air, and had precisely the same result. The alkaline water which I procured in this experiment was, beyond comparison, stronger to the smell, than any spirit of sal ammoniac that I had seen.
This experiment led me to attempt the making of spirit of sal ammoniac in a larger quant.i.ty, by impregnating distilled water with this alkaline air. For this purpose I filled a piece of a gun-barrel with the materials above-mentioned, and luted to the open end of it a small gla.s.s tube, one end of which was bent, and put within the mouth of a gla.s.s vessel, containing a quant.i.ty of distilled water upon quicksilver, standing in a bason of quicksilver, as in fig. 7. In these circ.u.mstances the heat of the fire, applied gradually, expelled the alkaline air, which, pa.s.sing through the tube, and the quicksilver, came at last to the water, which, in time, became fully saturated with it.
By this means I got a very strong alkaline liquor, from which I could again expel the alkaline air which I had put into it, whenever it happened to be more convenient to me to get it in that manner. This process may easily be performed in a still larger way; and by this means a liquor of the same nature with the volatile spirit of sal ammoniac, might be made much stronger, and much cheaper, than it is now made.