120 POPULAR SCIENCE MONTHLY. 



the experiment; and putting one measure of nitrous air to two measures 

 of this air, I foimd not only that it was diminished, but that it was 

 diminished quite as much as common air, and that the redness of the 

 mixture was likewise equal to that of a similar mixture of nitrous and 

 common air. 



After this I had no doubt but that the air from mercurius calcinatus 

 was fit for respiration, and that it Lad all the other properties of genuine 

 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 mercurius 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 preparation of this sub- 

 stance, 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, 1 likewise observed that the air which I had ex- 

 tracted 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 making the two others. But 

 to this circumstance 1 happened not to give much attention. 



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

 the word surprize, ami others of similar import; but I must go on in that 

 6tyle a little longer. For the next day I was more surprized 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, con- 

 fiequently, had it been common air it must have been made perfectly 

 noxious and entirely unfit for respiration or inflammation) 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 ;icquired a considerable degree of readiness 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 hap- 

 pened, for some other purpose, to have had a lighted candle before me 

 I should probably never have made the trial, and the whole train of my 

 future experiments relating to this kind of air might have been pre- 

 vented. 



Still, however, having no conception of the real cause of this 



