regained its transparence. These red fumes are due to portions of nitrous air and of air purer than ordinary, which are freed from the mercury salt and 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. 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. Priestley 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. without change in its quality or to any noticeable extent in its weight. So it is evident that the 426 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 cubic inches of nitrous air and 14 cubic inches of air better than ordinary 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.]
