OXYGEN AND THE NATURE OF ACIDS. 119 



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 altera- 

 tion 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 phlogisti- 

 cated 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 resem- 

 blance 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 experi- 

 ment 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 burn- 

 ing in it after long agitation in water, it occurred to me at last to make 



