This alkaline air being perfectly analogous 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 analogy 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 quantity and weight, water would acquire by being saturated with alkaline air, I put 1-1/4 grains of rain-water into a small glass 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 quantity 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 quantity, 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 glass tube, one end of which was bent, and put within the mouth of a glass vessel, containing a quantity of distilled water upon quicksilver, standing in a bason of quicksilver, as in fig. 7. In these circumstances the heat of the fire, applied gradually, expelled the alkaline air, which, passing 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.
Having satisfied myself with respect to the relation that alkaline air bears to water, I was impatient to find what would be the consequence of mixing this new air with the other kinds with which I was acquainted before, and especially with acid air; having a notion that these two airs, being of opposite natures, might compose a neutral air, and perhaps the very same thing with common air. But the moment that these two kinds of air came into contact, a beautiful white cloud was formed, and presently filled the whole vessel in which they were contained. At the same time the quantity of air began to diminish, and, at length, when the cloud was subsided, there appeared to be formed a solid while salt, which was found to be the common sal ammoniac, or the marine acid united to the volatile alkali.
The first quantity that I produced immediately deliquesced, upon being exposed to the common air; but if it was exposed in a very dry and warm place, it almost all evaporated, in a white cloud. I have, however, since, from the same materials, produced the salt above-mentioned in a state not subject to deliquesce or evaporate. This difference, I find, is owing to the proportion of the two kinds of air in the compound. It is only volatile when there is more than a due proportion of either of the constituent parts. In these cases the smell of the salts is extremely pungent, but very different from one another; being manifestly acid, or alkaline, according to the prevalence of each of these airs respectively.
Nitrous air admitted to alkaline air likewise occasioned a whitish cloud, and part of the air was absorbed; but it presently grew clear again; leaving only a little dimness on the sides of the vessel. This, however, might be a kind of salt, formed by the union of the two kinds of air. There was no other salt formed that I could perceive. Water being admitted to this mixture of nitrous and alkaline air presently absorbed the latter, and left the former possessed of its peculiar properties.
Fixed air admitted to alkaline air formed oblong and slender crystals, which crossed one another, and covered the sides of the vessel in the form of net-work. These crystals must be the same thing with the volatile alkalis which chemists get in a solid form, by the distillation of sal ammoniac with fixed alkaline salts.