Beginning with _water_, which, from preceding observations, I knew would imbibe it, and become impregnated with it; I found that 2-1/2 grains of rain-water absorbed three ounce measures of this air, after which it was increased one third in its bulk, and weighed twice as much as before; so that this concentrated vapour seems to be twice as heavy as rain-water: Water impregnated with it makes the strongest spirit of salt that I have seen, dissolving iron with the most rapidity. Consequently, two thirds of the best spirit of salt is nothing more than mere phlegm or water. Iron filings, being admitted to this air, were dissolved by it pretty fast, half of the air disappearing, and the other half becoming inflammable air, not absorbed by water. Putting chalk to it, fixed air was produced. I had not introduced many substances to this air, before I discovered that it had an affinity with _phlogiston_, so that it would deprive other substances of it, and form with it such an union as constitutes inflammable air; which seems to shew, that inflammable air universally consists of the union of some acid vapour with phlogiston. Inflammable air was produced, when to this acid air I put spirit of wine, oil of olives, oil of turpentine, charcoal, phosphorus, bees-wax, and even sulphur. This last observation, I own, surprized me; for, the marine acid being reckoned the weakest of the three mineral acids, I did not think that it had been capable of dislodging the oil of vitriol from this substance; but I found that it had the very same effect both upon alum and nitre; the vitriolic acid in the former case, and the nitrous in the latter, giving place to the stronger vapour of spirit of salt. The rust of iron, and the precipitate of nitrous air made from copper, also imbibed this air very fast, and the little that remained of it was inflammable air; which proves, that these calces contain phlogiston. It seems also to be pretty evident, from this experiment, that the precipitate above mentioned is a real calx of the metal, by the solution of which the nitrous air is generated. As some remarkable circumstances attend the absorption of this acid air, by the substances above-mentioned, I shall briefly mention them. Spirit of wine absorbs this air as readily as water itself, and is increased in bulk by that means. Also, when it is saturated, it dissolves iron with as much rapidity, and still continues inflammable. Oil of olives absorbs this air very slowly, and at the same time, it turns almost black, and becomes glutinous. It is also less miscible with water, and acquires a very disagreeable smell. By continuing upon the surface of the water, it became white, and its offensive smell went off in a few days.