It is something remarkable, though I never attended to it particularly before I made these last experiments, and it may tend to throw some light upon them, that when a candle is extinguished, as it never fails to be, in nitrous air, the flame seems to be a little enlarged at its edges, by another bluish flame added to it, just before its extinction.
It is proper to observe in this place, that the electric spark taken in nitrous air diminishes it to one fourth of its original quant.i.ty, which is about the quant.i.ty of its diminution by iron filings and brimstone, and also by liver of sulphur without heat. The air is also brought by electricity to the same state as it is by iron filings and brimstone, not diminishing common air. If the electric spark be taken in it when it is confined by water tinged with archil, it is presently changed from blue to red, and that to a very great degree.
When the iron nails or wires, which I have used to diminish nitrous air, had done their office, I laid them aside, not suspecting that they could be of any other philosophical use; but after having lain exposed to the open air almost a fortnight; having, for some other purpose, put some of them into a vessel containing common air, standing inverted, and immersed in water, I was surprized to observe that the air in which they were confined was diminished. The diminution proceeded so fast, that the process was completed in about twenty-four hours; for in that time the air was diminished about one fifth, so that it made no effervescence with nitrous air, and was, therefore, no doubt, highly noxious, like air diminished by any other process.
This experiment I have repeated a great number of times, with the same phials, filled with nails or wires that have been suffered to rust in nitrous air, but their power of diminishing common air grows less and less continually. How long it will be before it is quite exhausted I cannot tell. This diminution of air I conclude must arise from the phlogiston, either of the nitrous air or the iron, being some way entangled in the rust, in which the wires were encrusted, and afterwards getting loose from it.
To the experiments upon iron filings and brimstone in nitrous air, I must add, that when a pot full of this mixture had absorbed as much as it could of a jar of nitrous air (which is about three fourths of the whole) I put fresh nitrous air to it, and it continued to absorb, till three or four jars full of it disappeared; but the absorption was exceedingly slow at the last. Also when I drew this pot through the water, and admitted fresh nitrous air to it, it absorbed another jar full, and then ceased. But when I sc.r.a.ped off the outer surface of this mixture, which had been so long exposed to the nitrous air, the remainder absorbed more of the air.
When I took the top of the mixture which I had sc.r.a.ped off and threw upon it the focus of a burning-gla.s.s, the air in which it was confined was diminished, and became quite noxious; yet when I endeavoured to get air from this matter in a jar full of quicksilver, I was able to procure little or nothing.
It is not a little remarkable that nitrous air diminished by iron filings and brimstone, which is about one fourth, cannot, by agitation in water, be diminished much farther; whereas pure nitrous air may, by the same process, be diminished to one twentieth of its whole bulk, and perhaps much more. This is similar to the effect of the same mixture, and of phlogiston in other cases, on fixed air; for it so far changes its const.i.tution, that it is afterwards incapable of mixing with water.
It is similar also to the effect of phlogiston in acid air, which of itself is almost instantly absorbed by water; but by this addition it is first converted into inflammable air, which does not readily mix with water, and which, by long agitation in water, becomes of another const.i.tution, still less miscible with water.
I shall close this section with a few other observations of a miscellaneous nature.
Nitrous air is as much diminished both by iron filings, and also by liver of sulphur, when confined in quicksilver, as when it is exposed to water.
Distilled water tinged blue with the juice of turnsole becomes red on being impregnated with nitrous air; but by being exposed a week or a fortnight to the common atmosphere, in open and shallow vessels, it recovers its blue colour; though, in that time, the greater part of the water will be evaporated. This shews that in time nitrous air escapes from the water with which it is combined, just as fixed air does, though by no means so readily[14].
Having dissolved silver, copper, and iron in equal quant.i.ties of spirit of nitre diluted with water, the quant.i.ties of nitrous air produced from them were in the following proportion; from iron 8, from copper 6-1/4, from silver 6. In about the same proportion also it was necessary to mix water with the spirit of nitre in each case, in order to make it dissolve these metals with equal rapidity, silver requiring the least water, and iron the most.
Phosphorus gave no light in nitrous air, and did not take away from its power of diminishing common air; only when the redness of the mixture went off, the vessel in which it was made was filled with white fumes, as if there had been some volatile alkali in it. The phosphorus itself was unchanged.
There is something remarkable in the effect of nitrous air on _insects_ that are put into it. I observed before that this kind of air is as noxious as any whatever, a mouse dying the moment it is put into it; but frogs and snails (and therefore, probably, other animals whose respiration is not frequent) will bear being exposed to it a considerable time, though they die at length. A frog put into nitrous air struggled much for two or three minutes, and moved now and then for a quarter of an hour, after which it was taken out, but did not recover.
_Wasps_ always died the moment they were put into the nitrous air. I could never observe that they made the least motion in it, nor could they be recovered to life afterwards. This was also the case in general with _spiders_, _flies_, and _b.u.t.terflies_. Sometimes, however, spiders would recover after being exposed about a minute to this kind of air.
Considering how fatal nitrous air is to insects, and likewise its great antiseptic power, I conceived that considerable use might be made of it in medicine, especially in the form of _clysters_, in which fixed air had been applied with some success; and in order to try whether the bowels of an animal would bear the injection of it, I contrived, with the help of Mr. Hey, to convey a quant.i.ty of it up the a.n.u.s of a dog.
But he gave manifest signs of uneasiness, as long as he retained it, which was a considerable time, though in a few hours afterwards he was as lively as ever, and seemed to have suffered nothing from the operation.
Perhaps if nitrous air was diluted either with common air, or fixed air, the bowels might bear it better, and still it might be destructive to _worms_ of all kinds, and be of use to check or correct putrefaction in the intestinal ca.n.a.l, or other parts of the system. I repeat it once more that, being no physician, I run no risk by such proposals as these; and I cannot help flattering myself that, in time, very great medicinal use will be made of the application of these different kinds of air to the animal system. Let ingenious physicians attend to this subject, and endeavour to lay hold of the new _handle_ which is now presented them, before it be seized by rash empiricks; who, by an indiscriminate and injudicious application, often ruin the credit of things and processes which might otherwise make an useful addition to the _materia_ and _ars medica_.
In the first publication of my papers, having experienced the remarkable antiseptic power of nitrous air, I proposed an attempt to preserve anatomical preparations, &c. by means of it; but Mr. Hey, who made the trial, found that, after some months, various animal substances were shriveled, and did not preserve their natural forms in this kind of air.
FOOTNOTES:
[13] The result of several of these experiments I had the pleasure of trying in the presence of the celebrated Mr. De Luc of Geneva, when he was upon a visit to Lord Shelburne in Wiltshire.
[14] I have not repeated this experiment with that variation of circ.u.mstances which an attention to Mr. Bewley"s observation will suggest.
SECTION IV.
_Of MARINE ACID AIR._
In my former experiments on this species of air I procured it from spirit of salt, but I have since hit upon a much less expensive method of getting it, by having recourse to the process by which the spirit of salt is itself originally made. For this purpose I fill a small phial with common salt, pour upon it a small quant.i.ty of concentrated oil of vitriol, and receive the fumes emitted by it in a vessel previously filled with quicksilver, and standing in a bason of quicksilver, in which it appears in the form of a perfectly _transparent air_, being precisely the same thing with that which I had before expelled from the spirit of salt.
This method of procuring acid air is the more convenient, as a phial, once prepared in this manner, will suffice, for common experiments, many weeks; especially if a little more oil of vitriol be occasionally put to it. It only requires a little more heat at the last than at the first.
Indeed, at the first, the heat of a person"s hand will often be sufficient to make it throw out the vapour. In warm weather it will even keep smoking many days without the application of any other heat.
On this account, it should be placed where there are no instruments, or any thing of metal, that can be corroded by this acid vapour. It is from dear-bought experience that I give this advice. It may easily be perceived when this phial is throwing out this acid vapour, as it always appears, in the open air, in the form of a light cloud; owing, I suppose, to the acid attracting to itself, and uniting with, the moisture that is in the common atmosphere.
By this process I even made a stronger spirit of salt than can be procured in any other way. For having a little water in the vessel which contains the quicksilver, it imbibes the acid vapour, and at length becomes truly saturated with it. Having, in this manner, impregnated pure water with acid air, I could afterwards expel the same air from it, as from common spirit of salt.
I observed before that this acid vapour, or air, has a strong affinity with _phlogiston_, so that it decomposes many substances which contain it, and with them forms a permanently inflammable air, no more liable to be imbibed by water than inflammable air procured by any other process, being in fact the very same thing; and that, in some cases, it even dislodges spirit of nitre and oil of vitriol, which in general appear to be stronger acids than itself. I have since observed that, by giving it more time, it will extract phlogiston from substances from which I at first concluded that it was not able to do it, as from dry wood, crusts of bread not burnt, dry flesh, and what is more extraordinary from flints. As there was something peculiar to itself in the process or result of each of these experiments, it may not be improper to mention them distinctly.
Pieces of dry _cork wood_ being put to the acid air, a small quant.i.ty remained not imbibed by water, and was inflammable.
Very dry pieces of _oak_, being exposed to this air a day and a night, after imbibing a considerable quant.i.ty of it, produced air which was inflammable indeed, but in the slightest degree imaginable. It seemed to be very nearly in the state of common air.
A piece of _ivory_ imbibed the acid vapour very slowly. In a day and a night, however, about half an ounce measure of permanent air was produced, and it was pretty strongly inflammable. The ivory was not discoloured, but was rendered superficially soft, and clammy, tasting very acid.
Pieces of _beef_, roasted, and made quite dry, but not burnt, absorbed the acid vapour slowly; and when it had continued in this situation all night, from five ounce measures of the air, half a measure was permanent, and pretty strongly inflammable. This experiment succeeded a second time exactly in the same manner; but when I used pieces of white dry _chicken-flesh_ though I allowed the same time, and in other respects the process seemed to go on in the same manner, I could not perceive that any part of the remaining air was inflammable.
Some pieces of a whitish kind of _flint_, being put into a quant.i.ty of acid air, imbibed but a very little of it in a day and a night; but of 2-1/2 ounce measures of it, about half a measure remained unabsorbed by water, and this was strongly inflammable, taking fire just like an equal mixture of inflammable and common air. At another time, however, I could not procure any inflammable air by this means, but to what circ.u.mstance these different results were owing I cannot tell.
That inflammable air is produced from _charcoal_ in acid air I observed before. I have since found that it may likewise be procured from _pit coal_, without being charred.
Inflammable air I had also observed to arise from the exposure of spirit of wine, and various _oily_ substances, to the vapour of spirit of salt.
I have since made others of a similar nature, and as peculiar circ.u.mstances attended some of these experiments, I shall recite them more at large.
_Essential oil of mint_ absorbed this air pretty fast, and presently became of a deep brown colour. When it was taken out of this air it was of the consistence of treacle, and sunk in water, smelling differently from what it did before; but still the smell of the mint was predominant. Very little or none of the air was fixed, so as to become inflammable; but more time would probably have produced this effect.
_Oil of turpentine_ was also much thickened, and became of a deep brown colour, by being saturated with acid air.
_Ether_ absorbed acid air very fast, and became first of a turbid white, and then of a yellow and brown colour. In one night a considerable quant.i.ty of permanent air was produced, and it was strongly inflammable.
Having, at one time, fully saturated a quant.i.ty of ether with acid air, I admitted bubbles of common air to it, through the quicksilver, by which it was confined, and observed that white fumes were made in it, at the entrance of every bubble, for a considerable time.
At another time, having fully saturated a small quant.i.ty of ether with acid air, and having left the phial in which it was contained nearly full of the air, and inverted, it was by some accident overturned; when, instantly, the whole room was filled with a visible fume, like a white cloud, which had very much the smell of ether, but peculiarly offensive.
Opening the door and window of the room, this light cloud filled a long pa.s.sage, and another room. In the mean time the ether was seemingly all vanished, but some time after the surface of the quicksilver in which the experiment had been made was covered with a liquor that tasted very acid; arising, probably, from the moisture in the atmosphere attracted by the acid vapour with which the ether had been impregnated.
This visible cloud I attribute to the union of the moisture in the atmosphere with the compound of the acid air and ether. I have since saturated other quant.i.ties of ether with acid air, and found it to be exceedingly volatile, and inflammable. Its exhalation was also visible, but not in so great a degree as in the case above mentioned.
_Camphor_ was presently reduced into a fluid state by imbibing acid air, but there seemed to be something of a whitish sediment in it. After continuing two days in this situation I admitted water to it; immediately upon which the camphor resumed its former solid state, and, to appearance, was the very same substance that it had been before; but the taste of it was acid, and a very small part of the air was permanent, and slightly inflammable.
The acid air seemed to make no impression upon a piece of Derbyshire _spar_, of a very dark colour, and which, therefore, seemed to contain a good deal of phlogiston.
As the acid air has so near an affinity with phlogiston, I expected that the fumes of _liver of sulphur_, which chemists agree to be phlogistic, would have united with it, so as to form inflammable air; but I was disappointed in that expectation. This substance imbibed half of the acid air to which it was introduced: one fourth of the remainder, after standing one day in quicksilver, was imbibed by water, and what was left extinguished a candle. This experiment, however, seems to prove that acid air and phlogiston may form a permanent kind of air that is not inflammable. Perhaps it may be air in such a state as common air loaded with phlogiston, and from which the fixed air has been precipitated. Or rather, it may be the same thing with inflammable air, that has lost its inflammability by long standing in water. It well deserves a farther examination.
The following experiments are those in which the _stronger acids_ were made use of, and therefore they may a.s.sist us farther to ascertain their affinities with certain substances, with respect to this marine acid in the form of air.
I put a quant.i.ty of strong concentrated _oil of vitriol_ to acid air, but it was not at all affected by it in a day and a night. In order to try whether it would not have more power in a more condensed state, I compressed it with an additional atmosphere; but upon taking off this pressure, the air expanded again, and appeared to be not at all diminished. I also put a quant.i.ty of strong _spirit of nitre_ to it without any sensible effect. We may conclude, therefore, that the marine acid, in this form of air, is not able to dislodge the other acids from their union with water.
_Blue vitriol_, which is formed by the union of the vitriolic acid with copper, turned to a dark green the moment that it was put to the acid air, which it absorbed, though slowly. Two pieces, as big as small nuts, absorbed three ounce measures of the air in about half an hour. The green colour was very superficial; for it was easily wiped or washed off.