CHEMISTRY OF THE EIGHTEENTH CENTURY. 363 



when I took it out quite lively and vigorous. Measuring the air the 

 next day, I found it to be reduced from one and a half to two-thirds 

 of an ounce measure. And after this, if I remember well (for in my 

 register of the day I only find it noted that it was considerably diminished 

 by nitrous air) it was nearly as good as common air. It was evident, 

 indeed, from the mouse having been taken out quite vigorous, that the 

 air could not have been rendered very noxious. 



" For my further satisfaction I procured another mouse, and putting 

 it into less than two ounce measures of air extracted from mercurius 

 calcinatus and air from red precipitate (which, having found them to 

 be of the same quality, I had mixed together), it lived three-quarters 

 of an hour. But not having had the precaution to set the vessel in a 

 warm place, I suspect that the mouse died of cold " (Priestley passed 

 up the mice into the inverted vessel of gas through the water). " How- 

 ever, as it had lived three times as long as it could probably have lived 

 in the same quantity of common air, and I did not expect much accu- 

 racy from this kind of 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 accu- 

 racy as I could by the test of nitrous 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 dimi- 

 nution could not proceed much further, I then added only half a 

 measure of nitrous air. By this 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 vras. Five measures brought it pretty exactly to its original dimen- 

 sions. 



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

 the same proportion as that from mtrcurius caldnatus^ 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 

 dimensions 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 dimen- 

 sions, I concluded that it was between four and five times as good as 

 common air. It will be seen that I have since procured air purer 

 than this." 



ANTOINE LAURENT LAVOISIER (1743 1794) was born at Paris, and 

 his father, a wealthy merchant, was in a position to afford him the best 

 education. He showed at an early age a decided taste for science, 



