i2 4 POPULAR SCIENCE MONTHLY. 



regained its transparence.* Having put to one side the air which had 

 been given off during the period of the red fumes, I found ten to twelve 

 inches of air very different from what had been given off up till then, 

 and apparently differing from ordinary air only in that lights burned 

 -lightly better in it. At the same time the mercury salt had turned to 

 a fine red precipitate, and, keeping it at a moderate heat, I obtained 

 at the end of seven hours 224 cubic inches of air much purer than 

 ordinary air, in which a light burned with a much brighter, larger and 

 brilliant or more active flame. This air, from all its characteristics, I 

 could riot but recognize as the same that I had extracted from calx of 

 mercury, known as mercury precipitatum per se; the same that M. Priest- 

 ley extracted from a number of substances by treating them with spirits 

 of nitre. In proportion as this air had been freed, the mercury had 

 been reduced, and I found again, within a few grains, the two ounces 

 one dram of mercury which I had dissolved. The slight loss may have 

 been due to a little yellow and red sublimate which clung to the upper 

 part of the retort. 



The mercury came out of this experiment as it went in, that is. with- 

 out change in its quality or to any noticeable extent in its weight. So it 

 is evident that the 42G cubic inches of air which I had obtained could 

 have been produced only by the decomposition of the acid of nitre. I 

 was then right in concluding from these facts that two ounces of acid of 

 nitre are composed, first, of 190 cubic inches of nitrous air; second, of 

 12 cubic inches of ordinary air; third, of 224 cubic inches of air better 

 than ordinary air; fourth, of phlegm; but as it was proved from M. 

 Priestley's experiments, that the small amount of common air which I 

 had obtained could be nothing save air better than common air, the 

 superior quality of which had been altered by mixture with nitrous air 

 in the transition or passing from one to the other, I can determine the 

 amount of these two airs before their mixture and suppose that the 12 

 cubic inches of common air which I got were due to a mixture of 30 

 •ill lie inches of nitrous air and 11 cubic inches of air better than ordi- 

 nary air. 



After thus determining these quantities, we get as the product of 

 two ounces of acid of nitre: 



Nitrous air 226 cubic inches. 



Purest air 238 " " 



Total 464 



[Lavoisier here uses the estimated weight of the gases found to 

 decide the composition by weight of nitric acid.] 



1 l hese red fumes are due to portions <>f nitrons air and of .air jmrer than ordinary, which 

 are freed from the mercury salt am] which combine and form the acid of nitre. The force of 

 this explanation will he fully felt only after the entire memoir has been read. 



