JOSEPH PRIESTLEY 99 



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 this phe- 

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

 property that was peculiar to air that was extracted from these sub- 

 stances, and adventitious; and I always spoke of the air to my ac- 

 quaintance 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 I procured a mouse, and put it into a glass 

 vessel, containing two ounce-measures of the air from mercuris calci- 

 natus. Had it been common air, a full-grown mouse, as this was, 

 would have lived in it about a quarter of an hour. In this air, how- 

 ever, my mouse lived a full half hour ; and though it was taken out 

 seemingly dead, it appeared to have been only exceedingly chilled ; for, 

 upon being held to fire, it presently revived, and appeared not to have 

 received any harm from the experiment. 



By this I was confirmed in my conclusion, that the air extracted 

 from mercuriiis calcinatus, &c., was, at least, as good as common air ; 

 but I did not certainly conclude that it was any better; because, 

 though one mouse would live only a quarter of an hour in a given 

 quantity of air, I knew it was not impossible but that another mouse 

 might have lived in it half an hour ; so little accuracy is there in this 

 method of ascertaining the goodness of air ; and indeed I have never 

 had recourse to it for my own satisfaction, since the discovery of that 

 most ready, accurate, and elegant test that nitrous air furnishes. But 

 in this case I had a view to pubHshing the most generally satisfactory 

 account of my experiments that the nature of the thing would ad- 

 mit of. 



This experiment with the mouse, when I had reflected upon it some 

 time, gave me so much suspicion that the air into which I had put it 

 was better than common air, that I was induced, the day after, to 

 apply the test of nitrous air to a small part of that very quantity of air 

 which the mouse had breathed so long ; so that, had it been common 

 air, I was satisfied it must have been very nearly, if not altogether, as 



