362 HISTORY OF SCIENCE. 



as this was would have lived in it about a quarter of an hour. In this 

 air, however, 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 the 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 mercurius calcinatus, etc., 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 (nitric oxide) 

 furnishes. But in this case I had a view to publishing the most gene- 

 rally satisfactory account of my experiments that the nature of the 

 thing would admit 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 alto- 

 gether, as noxious as possible, so as not to be affected by nitrous air ; 

 when, to my surprise again, I found that though it had been breathed 

 so long, it was still better than common air. For, after mixing it with 

 nitrous air in the usual proportion of two to one, it was diminished in 

 the proportion of four and a half to three and a half; that is, the 

 nitrous air had made it two-ninths less than before, and this in a very 

 short space of time ; whereas I had never found that in the longest 

 time any common air was reduced more than one-fifth of its bulk by 

 any proportion of nitrous air, nor more than one-fourth by any phlo- 

 gistic process whatever. Thinking of this extraordinary fact upon my 

 pillow the next morning, I put another measure of nitrous air to the 

 same mixture, and, to my utter astonishment, found that it was further 

 diminished to almost one-half of its original quantity. I then put a 

 third measure to it ; but this did not diminish it any further, but left 

 it one measure less than it was -even after the mouse had been taken 

 out of it. 



" Being now fully satisfied that this air, even after the mouse had 

 breathed it half an hour, was much better than common air, and 

 having a quantity of it still left, sufficient for the experiment viz., an 

 ounce measure and a half I put the mouse into it ; when I observed 

 that it seemed to feel no shock upon being put into it, evident signs 

 of which would have been visible if the air had not been very whole- 

 some, but that it remained perfectly at its ease another full half-hour, 



