JOSEPH PRIESTLEY loi 



from this kind of a test, I did not think it necessary to make any more 

 experiments with mice. 



Being now fully satisfied of the superior goodness of this kind of 

 air, I proceeded to measure that degree of purity, with as much ac- 

 curacy as I could, by the test of nitrous air ; and I began with putting 

 one measure of nitrous air to two measures of this air, as if I had been 

 examining common air ; and now I observed that the diminution was 

 evidently greater than common air would have suffered by the same 

 treatment. A second measure of nitrous air reduced it to two-thirds 

 of its original quantity, and a third measure to one-half. Suspecting 

 that the diminution could not proceed much farther, I then added 

 only half a measure of nitrous air, by which it was diminished still 

 more; but not much, and another half-measure made it more than 

 half of its original quantity ; so that, in this case, two measures of this 

 air took more than two measures of nitrous air, and yet remained 

 less than half of what it was. Five measures brought it pretty exactly 

 to its original dimensions. 



At the same time, air from the red precipitate was diminished in the 

 same proportion as that from mercurius calcinatus, five measures of 

 nitrous air being received by two measures of this without any increase 

 of dimensions. Now as common air takes about one-half of its bulk 

 of nitrous air, before it begins to receive any addition to its dimen- 

 sions from more nitrous air, and this air took more than four half- 

 measures before it ceased to be diminished by more nitrous air, and 

 even five half-measures made no addition to its original dimensions, 

 I conclude that it was between four and five times as good as common 

 air. It will be seen that I have since procured air better than this, 

 even between five and six times as good as the best common air that 

 I have ever met with. 



