98 CLASSICS OF MODERN SCIENCE 

 was fit for respiration, and that it had all the other properties of gen- 

 uine common air. But I did not take notice of what I might have 

 observed, if I had not been so fully possessed by the notion of there 

 being no air better than common air, that the redness was really 

 deeper, and the diminution something greater than common air would 

 have admitted. 



Moreover, this advance in the way of truth, in reality, threw me 

 back into error, making me give up the hypothesis I had first formed, 

 viz. that the mercurhis calcinatus had extracted spirit of nitre from 

 the air ; for I now concluded, that all the constituent parts of the air 

 were equally, and in their proper proportion, imbibed in the prepara- 

 tion of this substance, and also in the process of making red lead. 

 For at the same time that I made the above mentioned experiment on 

 the air from mercurius calcinatus, I likewise observed that the air 

 which I had extracted from red lead, after the fixed air was washed 

 out of it, was of the same nature, being diminished by nitrous air like 

 common air : but, at the same time, I was puzzled to find that air from 

 the red precipitate was diminished in the same manner, though the 

 process for making this substance is quite different from that of mak- 

 ing the two others. But to this circumstance I happened not to give 

 much attention. 



I wish my reader be not quite tired with the frequent repetition of 

 the word surprise, and others of similar import ; but I must go on in 

 that style a little longer. For the next day I was more surprised than 

 ever I had been before, with finding that, after the above-mentioned 

 mixture of nitrous air and the air from mercurius calcinatus, had 

 stood all night, (in which time the whole diminution must have taken 

 place; and, consequently, had it been common air, it must have been 

 made perfectly noxious, and entirely unfit for respiration or inflamma- 

 tion) a candle burned in it, and even better than in common air. 



I cannot, at this distance of time, recollect what it was that I had 

 in view in making this experiment ; but I know I had no expectation of 

 the real issue of it. Having acquired a considerable degree of readi- 

 ness in making experiments of this kind, a very slight and evanescent 

 motive would be sufficient to induce me to do it. If, however, I had 

 not happened, for some other purpose, to have had a lighted candle 

 before me I should probably never have made the trial ; and the whole 



