CHEMISTRY OF THE EIGHTEENTH CENTURY. 361 



air better than common air, that the redness was really deeper, and 

 the diminution something greater than common air would have ad- 

 mitted. 



" I now concluded that all the constituent parts of the air were 

 equally, and in their proper proportion, imbibed in the preparation of 

 this substance (mercurius calcinatus), 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 

 (carbonic acid) 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 cir- 

 cumstance 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, by 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 in inflammation) a 

 candle burned in it even better than in common air." (A surplus of 

 oxygen remained^] 



" 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 

 readiness in making experiments of this kind, a very slight and evanes- 

 cent 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 train of my future experiments relating to this kind of air 

 might have been prevented. 



" Still, however, having no conception of the real cause of the phe- 

 nomenon, I considered it as something very extraordinary, but as a 

 property that was peculiar to air extracted from these substances, and 

 adventitious ; and I always spoke of the air to my acquaintance as 

 being substantially the same thing with common air. I particularly 

 remember my telling Dr. Price that I was myself perfectly satisfied of 

 its being common air, as it appeared to be so by the test of nitrous 

 air, though, for the satisfaction of others, I wanted a mouse to make 

 the proof quite complete. 



" On the 8th of this month (March, 1775) I procured a mouse, and 

 put it into a glass vessel containing two ounce measures of the air from 

 mercurius calcinatus. Had it been common air, a full-grown mouse 



