Experiments and Observations on Different Kinds of Air — PART II, Sect. VI. Of Fixed Air, Sect. VII. Miscellaneous Experiments

SECTION VI.

_Of FIXED AIR.

_ The additions I have made to my observations on _fixed air_ are neither numerous nor considerable.

The most important of them is a confirmation of my conjecture, that fixed air is capable of forming an union with phlogiston, and thereby becoming a kind of air that is not miscible with water.

I had produced this effect before by means of iron filings and brimstone, fermenting in this kind of air; but I have since had a much more decisive and elegant proof of it by _electricity_.

For after taking a small electric explosion, for about an hour, in the space of an inch of fixed air, confined in a glass tube one tenth of an inch in diameter, fig. 16, I

found that when water was admitted to it, only one fourth of the air was imbibed.

Probably the whole of it would have been rendered immiscible in water, if the electrical operation had been continued a sufficient time.

This air continued several days in water, and was even agitated in water without any farther diminution.

It was not, however, common air, for it was not diminished by nitrous air.

By means of iron filings and brimstone I have, since my former experiments, procured a considerable quantity of this kind of air in a method something different from that which I used before.

For having placed a pot of this mixture under a receiver, and exhausted it with a pump of Mr. Smeaton's construction, I filled it with fixed air, and then left it plunged under water; so that no common air could have access to it.

In this manner, and in about a week, there was, as near as I can recollect, one sixth, or at least one eighth of the whole converted into a permanent air, not imbibed by water.

From this experiment I expected that the same effect would have been produced on fixed air by the fumes of _liver of sulphur_; but I was disappointed in that expectation, which surprised me not a little;

though this corresponds in some measure, to the effect of phlogiston exhaled from this substance on acid air.

Perhaps more time may be requisite for this purpose, for this process was not continued more than a day and a night.

Iron filings and brimstone, I have observed, ferment with great heat in nitrous air, and I have since observed that this process is attended with greater heat in fixed air than in common air.

Though fixed air incorporated with water dissolves iron, fixed air without water has no such power, as I observed before.

I imagined that, if it could have dissolved iron, the phlogiston would have united with the air, and have made it immiscible with water, as in the former instances; but after being confined in a phial full of nails from the 15th of December to the 4th of October following, neither the iron nor the air appeared to have been affected by their mutual contact.

Having exposed equal quantities of common and fixed air, in equal and similar cylindrical glass vessels, to equal degrees of heat, by placing them before a fire, and frequently changing their situations, I observed that they were expanded exactly alike, and when removed from the fire they both recovered their former dimensions.

Having had some small suspicion that liver of sulphur, besides emitting phlogiston, might also yield some fixed air (which is known to be contained in the salt of tartar from which it is made) I mixed the two ingredients, viz.

salt of tartar and brimstone, and putting them into a thin phial, and applying the flame of a candle to it, so as to form the liver of sulphur, I received the air that came from it in this process in a vessel of quicksilver.

In this manner I procured a very considerable quantity of fixed air, so that I judged it was all discharged from the tartar.

But though it is possible that a small quantity of it may remain in liver of sulphur, when it is made in the most perfect manner, it is not probable that it can be expelled without heat.

SECTION VII. MISCELLANEOUS EXPERIMENTS.

1. It is something extraordinary that, though ether, as I found, cannot be made to assume the form of air (the vapour arising from it by heat, being soon condensed by cold, even in quicksilver) yet that a very small quantity of ether put to any kind of air, except the acid, and alkaline, which it imbibes, almost instantly doubles the apparent quantity of it;

but upon passing this air through water, it is presently reduced to its original quantity again, with little or no change of quality.

I put about the quantity of half a nut-shell full of ether, inclosed in a glass 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 space 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 passing 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 quantity 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 passing 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 circumstances 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 quantity 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 quantity 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 quantity, 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 quantity 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-glass fired the gunpowder which had been previously put into it.

By this means I could fire a greater quantity of gunpowder in a small quantity 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 assistance, 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 glass 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 quantity 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 quantity 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 circumstances was necessarily mixed with common air.

A candle would not burn in it.

SECTION VIII.