Experiments and Observations on Different Kinds of Air Part 6

Hey, an ingenious surgeon in Leeds a case presently occurred, in which he had an opportunity of giving it a trial; and mentioning it to Dr.

Hird and Dr. Crowther, two physicians who attended the patient, they approved the scheme, and it was put in execution; both by applying the fixed air by way of clyster, and at the same time making the patient drink plentifully of liquors strongly impregnated with it. The event was such, that I requested Mr. Hey to draw up a particular account of the case, describing the whole of the treatment, that the public might be satisfied that this new application of fixed air is perfectly safe, and also, have an opportunity of judging how far it had the effect which I expected from it; and as the application is new, and not unpromising, I shall subjoin his letter to me on the subject, by way of _Appendix_ to these papers.

When I began my inquires into the properties of different kinds of air, I engaged my friend Dr. Percival to attend to the _medicinal uses_ of them, being sensible that his knowledge of philosophy as well as of medicine would give him a singular advantage for this purpose. The result of his observations I shall also insert in the Appendix.

FOOTNOTES:

[5] Some time after these papers were first printed, I was pleased to find the same proposal in _Dr. Alexander's Experimental Essays_.

SECTION V.

_Of AIR in which a mixture of BRIMSTONE and FILINGS of IRON has stood._

Reading in Dr. Hales's account of his experiments, that there was a great diminution of the quant.i.ty of air in which _a mixture of powdered brimstone and filings of iron, made into a paste with water_, had stood, I repeated the experiment, and found the diminution greater than I had expected. This diminution of air is made as effectually, and as expeditiously, in quicksilver as in water; and it may be measured with the greatest accuracy, because there is neither any previous expansion or increase of the quant.i.ty of air, and because it is some time before this process begins to have any sensible effect. This diminution of air is various; but I have generally found it to be between one fifth and one fourth of the whole.

Air thus diminished is not heavier, but rather lighter than common air; and though lime-water does not become turbid when it is exposed to this air, it is probably owing to the formation of a selenitic salt, as was the case with the simple burning of brimstone above-mentioned. That something proceeding from the brimstone strongly affects the water which is confined in the same place with this mixture, is manifest from the very strong smell that it has of the volatile spirit of vitriol.

I conclude that the diminution of air by this, process is of the same kind with the diminution of it in the other cases, because when this mixture is put into air which has been previously diminished, either by the burning of candles, by respiration, or putrefaction, though it never fails to diminish it something more, it is, however, no farther than this process alone would have done it. If a fresh mixture be introduced into a quant.i.ty of air which had been reduced by a former mixture, it has little or no farther effect.

I once observed, that when a mixture of this kind was taken out of a quant.i.ty of air in which a candle had before burned out, and in which it had stood for several days, it was quite cold and black, as it always becomes in a confined place; but it presently grew very hot, smoaked copously, and smelled very offensively; and when it was cold, it was brown, like the rust of iron.

I once put a mixture of this kind to a quant.i.ty of inflammable air, made from iron, by which means it was diminished 1/9 or 1/10 in its bulk; but, as far as I could judge, it was still as inflammable as ever.

Another quant.i.ty of inflammable air was also reduced in the same proportion, by a mouse putrefying in it; but its inflammability was not seemingly lessened.

Air diminished by this mixture of iron filings and brimstone, is exceedingly noxious to animals, and I have not perceived that it grows any better by keeping in water. The smell of it is very pungent and offensive.

The quant.i.ty of this mixture which I made use of in the preceding experiments, was from two to four ounce measures; but I did not perceive, but that the diminution of the quant.i.ty of air (which was generally about twenty ounce measures) was as great with the smallest, as with the largest quant.i.ty. How small a quant.i.ty is necessary to diminish a given quant.i.ty of air to a _maximum_, I have made no experiments to ascertain.

As soon as this mixture of iron filings with, brimstone and water, begins to ferment, it also turns black, and begins to swell, and it continues to do so, till it occupies twice as much s.p.a.ce as it did at first. The force with which it expands is great; but how great it is I have not endeavoured to determine.

When this mixture is immersed in water, it generates no air, though it becomes black, and swells.

SECTION VI.

_Of NITROUS AIR._

Ever since I first read Dr. Hales's most excellent _Statical Essays_, I was particularly struck with that experiment of his, of which an account is given, VOL. I, p. 224. and VOL. II, p. 280. in which common air, and air generated from the Walton pyrites, by spirit of nitre, made a turbid red mixture, and in which part of the common air was absorbed; but I never expected to have the satisfaction of seeing this remarkable appearance, supposing it to be peculiar to that particular mineral.

Happening to mention this subject to the Hon. Mr. Cavendish, when I was in London, in the spring of the year 1772, he said that he did not imagine but that other kinds of pyrites, or the metals might answer as well, and that probably the red appearance of the mixture depended upon the spirit of nitre only. This encouraged me to attend to the subject; and having no pyrites, I began with the solution of the different metals in spirit of nitre, and catching the air which was generated in the solution, I presently found what I wanted, and a good deal more.

Beginning with the solution of bra.s.s, on the 4th of June 1772, I first found this remarkable species of air, only one effect of which, was casually observed by Dr. Hales; and he gave so little attention to it, and it has been so much unnoticed since his time, that, as far as I know, no name has been given to it. I therefore found myself, contrary to my first resolution, under an absolute necessity of giving a name to this kind of air myself. When I first began to speak and write of it to my friends, I happened to distinguish it by the name of _nitrous air_, because I had procured it by means of spirit of nitre only; and though I cannot say that I altogether like the term, neither myself nor any of my friends, to whom I have applied for the purpose, have been able to hit upon a better; so that I am obliged, after all, to content myself with it.

I have found that this kind of air is readily procured from iron, copper, bra.s.s, tin, silver, quicksilver, bis.m.u.th, and nickel, by the nitrous acid only, and from gold and the regulus of antimony by _aqua regia_. The circ.u.mstances attending the solution of each of these metals are various, but hardly worth mentioning, in treating of the properties of the _air_ which they yield; which, from what metal soever it is extracted, has, as far as I have been able to observe, the very same properties.

One of the most conspicuous properties of this kind of air is the great diminution of any quant.i.ty of common air with which it is mixed, attended with a turbid red, or deep orange colour, and a considerable heat. The _smell_ of it, also, is very strong, and remarkable, but very much resembling that of smoking spirit of nitre.

The diminution of a mixture of this and common air is not an equal diminution of both the kinds, which is all that Dr. Hales could observe, but of about one fifth of the common air, and as much of the nitrous air as is necessary to produce that effect; which, as I have found by many trials, is about one half as much as the original quant.i.ty of common air. For if one measure of nitrous air be put to two measures of common air, in a few minutes (by which time the effervescence will be over, and the mixture will have recovered its transparency) there will want about one ninth of the original two measures; and if both the kinds of air be very pure, the diminution will still go on slowly, till in a day or two, the whole will be reduced to one fifth less than the original quant.i.ty of common air. This farther diminution, by long standing, I had not observed at the time of the first publication of these papers.

I hardly know any experiment that is more adapted to amaze and surprize than this is, which exhibits a quant.i.ty of air, which, as it were, devours a quant.i.ty of another kind of air half as large as itself, and yet is so far from gaining any addition to its bulk, that it is considerably diminished by it. If, after this full saturation of common air with nitrous air, more nitrous air be put to it, it makes an addition equal to its own bulk, without producing the least redness, or any other visible effect.

If the smallest quant.i.ty of common air be put to any larger quant.i.ty of nitrous air, though the two together will not occupy so much s.p.a.ce as they did separately, yet the quant.i.ty will still be larger than that of the nitrous air only. One ounce measure of common air being put to near twenty ounce measures of nitrous air, made an addition to it of about half an ounce measure. This being a much greater proportion than the diminution of common air, in the former experiment, proves that part of the diminution in the former case is in the nitrous air. Besides, it will presently appear, that nitrous air is subject to a most remarkable diminution; and as common air, in a variety of other cases, suffers a diminution from one fifth to one fourth, I conclude, that in this case also it does not exceed that proportion, and therefore that the remainder of the diminution respects the nitrous air.

In order to judge whether the _water_ contributed to the diminution of this mixture of nitrous and common air, I made the whole process several times in quicksilver, using one third of nitrous, and two thirds of common air, as before. In this case the redness continued a very long time, and the diminution was not so great as when the mixtures had been made in water, there remaining one seventh more than the original quant.i.ty of common air.

This mixture stood all night upon the quicksilver; and the next morning I observed that it was no farther diminished upon the admission of water to it, nor by pouring it several times through the water, and letting it stand in water two days.

Another mixture, which had stood about six hours on the quicksilver, was diminished a little more upon the admission of water, but was never less than the original quant.i.ty of common air. In another case however, in which the mixture had stood but a very short time in quicksilver, the farther diminution, which took place upon the admission of water, was much more considerable; so that the diminution, upon the whole, was very nearly as great as if the process had been intirely in water.

It is evident from these experiments, that the diminution is in part owing to the absorption by the water; but that when the mixture is kept a long time, in a situation in which there is no water to absorb any part of it, it acquires a const.i.tution, by which it is afterwards incapable of being absorbed by water, or rather, there is an addition to the quant.i.ty of air by nitrous air produced by the solution of the quicksilver.

It will be seen, in the second part of this work, that, in the decomposition of nitrous air by its mixture with common air, there is nothing at hand when the process is made in quicksilver, with which the acid that entered into its composition can readily unite.

In order to determine whether the fixed part of common air was deposited in the diminution of it by nitrous air, I inclosed a vessel full of lime-water in the jar in which the process was made, but it occasioned no precipitation of the lime; and when the vessel was taken out, after it had been in that situation a whole day, the lime was easily precipitated by breathing into it as usual.

But though the precipitation of the lime was not sensible in this method of making the experiment, it is sufficiently so when the whole process is made in lime-water, as will be seen in the second part of this work; so that we have here another evidence of the deposition of fixed air from common air. I have made no alteration, however, in the preceding paragraph, because it may not be unuseful, as a caution to future experimenters.

It is exceedingly remarkable that this effervescence and diminution, occasioned by the mixture of nitrous air, is peculiar to common air, or _air fit for respiration_; and, as far as I can judge, from a great number of observations, is at least very nearly, if not exactly, in proportion to its fitness for this purpose; so that by this means the goodness of air may be distinguished much more accurately than it can be done by putting mice, or any other animals, to breathe in it.

This was a most agreeable discovery to me, as I hope it may be an useful one to the public; especially as, from this time, I had no occasion for so large a stock of mice as I had been used to keep for the purpose of these experiments, using them only in those which required to be very decisive; and in these cases I have seldom failed to know beforehand in what manner they would be affected.

It is also remarkable that, on whatever account air is unfit for respiration, this same test is equally applicable. Thus there is not the least effervescence between nitrous and fixed air, or inflammable air, or any species of diminished air. Also the degree of diminution being from nothing at all to more than one third of the whole of any quant.i.ty of air, we are, by this means, in possession of a prodigiously large _scale_, by which we may distinguish very small degrees of difference in the goodness of air.

I have not attended much to this circ.u.mstance, having used this test chiefly for greater differences; but, if I did not deceive myself, I have perceived a real difference in the air of my study, after a few persons have been with me in it, and the air on the outside of the house. Also a phial of air having been sent me, from the neighbourhood of York, it appeared not to be so good as the air near Leeds; that is, it was not diminished so much by an equal mixture of nitrous air, every other circ.u.mstance being as nearly the same as I could contrive. It may perhaps be possible, but I have not yet attempted it, to distinguish some of the different winds, or the air of different times of the year, &c. &c. by this test.

By means of this test I was able to determine what I was before in doubt about, viz. the _kind_ as well as the _degree_ of injury done to air by candles burning in it. I could not tell with certainty, by means of mice, whether it was at all injured with respect to respiration; and yet if nitrous air may be depended upon for furnis.h.i.+ng an accurate test, it must be rather more than one third worse than common air, and have been diminished by the same general cause of the other diminutions of air.

For when, after many trials, I put one measure of thoroughly putrid and highly noxious air, into the same vessel with two measures of good wholesome air, and into another vessel an equal quant.i.ty, viz. three measures of air in which a candle had burned out; and then put equal quant.i.ties of nitrous air to each of them, the latter was diminished rather more than the former.

It agrees with this observation, that _burned air_ is farther diminished both by putrefaction, and a mixture of iron filings and brimstone; and I therefore take it for granted by every other cause of the diminution of air. It is probable, therefore, that burned air is air so far loaded with phlogiston, as to be able to extinguish a candle, which it may do long before it is fully saturated.

Inflammable air with a mixture of nitrous air burns with a green flame.

This makes a very pleasing experiment when it is properly conducted. As, for some time, I chiefly made use of _copper_ for the generation of nitrous air, I first ascribed this circ.u.mstance to that property of this metal, by which it burns with a green flame; but I was presently satisfied that it must arise from the spirit of nitre, for the effect is the very same from which ever of the metals the nitrous air is extracted, all of which I tried for this purpose, even silver and gold.

A mixture of oil of vitriol and spirit of nitre in equal proportions dissolved iron, and the produce was nitrous air; but a less degree of spirit of nitre in the mixture produced air that was inflammable, and which burned with a green flame. It also tinged common air a little red, and diminished it, though not much.

The diminution of common air by a mixture of nitrous air, is not so extraordinary as the diminution which nitrous air itself is subject to from a mixture of iron filings and brimstone, made into a paste with water. This mixture, as I have already observed, diminishes common air between one fifth and one fourth, but has no such effect upon any kind of air that has been diminished, and rendered noxious by any other process; but when it is put to a quant.i.ty of nitrous air, it diminishes it so much, that no more than one fourth of the original quant.i.ty will be left.

The effect of this process is generally perceived in five or six hours, about which time the visible effervesence of the mixture begins; and in a very short time it advances so rapidly, that in about an hour almost the whole effect will have taken place. If it be suffered to stand a day or two longer, the air will still be diminished farther, but only a very little farther, in proportion to the first diminution. The gla.s.s jar, in which the air and this mixture have been confined, has generally been so much heated in this process, that I have not been able to touch it.

Nitrous air thus diminished has not so strong a smell as nitrous air itself, but smells just like common air in which the same mixture has stood; and it is not capable of being diminished any farther, by a fresh mixture of iron and brimstone.

Common air saturated with nitrous air is also no farther diminished by this mixture of iron filings and brimstone, though the mixture ferments with great heat, and swells very much in it.

Plants die very soon, both in nitrous air, and also in common air saturated with nitrous air, but especially in the former.