of it, an ounce-measure of air, which I observed to be not readily imbibed, either by the substance itself from which it had been expelled (for I suffered them to continue a long time together before I transferred the air to any other place) or by water, in which I suffered this air to stand a considerable time before* I made any experiment upon it.
In this air, as I had expected, a candle burned with a vivid flame; but what I observed new at this time (Nov. 19), and which surprized me no less than the fact I had discovered before, was that whereas a few moments' agitation in water will deprive the modified nitrous air of its property of admitting a candle to burn in it; yet, after more than ten times as much agitation as would be sufficient to produce this alteration in the nitrous air, no sensible change was produced in this. A candle still burned in it with a strong flame, and it did not in the least diminish common air, which I have observed that nitrous air, in this state, in some measure does.
But I was much more surprized when, after two days, in which this air had continued in contact with water (by which it was diminished about one twentieth of its bulk) I agitated it violently in water about five minutes and found that a candle still burned in it as well as in common air. The same degree of agitation would have made phlogisticated nitrous air fit for respiration indeed, but it would certainly have extinguished a candle.
These facts fully convinced me that there must be a very material difference between the constitution of the air from mercurius calcinatus and that of phlogisticated nitrous air, notwithstanding their resemblance in some particulars. But though I did not doubt that the air from mercurius calcinatus was fit for respiration after being agitated in water, as every kind of air without exception on which I had tried the experiment had been, I still did not suspect that it was respirable in the first instance; so far was I from having any idea of this air being what it really was, much superior in this respect to the air of the atmosphere.
In this ignorance of the real nature of this kind of air, I continued from this time (November) to the 1st of March following; having, in the meantime, been intent upon my experiments on the vitriolic acid air, above recited, and the various modifications of air produced by spirit of nitre, an account of which will follow. But in the course of this month I not only ascertained the nature of this kind of air, though very gradually, but was led by it to the complete discovery of the constitution of the air we breathe.
Till this 1st of March, 1775, I had so little suspicion of, the air from mercurius calcinatus, etc., being wholesome that I had not even thought of applying to it the test of nitrous air; but thinking (as my reader must imagine I frequently must have done) on the candle burning in it after long agitation in water, it occurred to me at last to make
