Priestley found that the metallic oxides when strongly heated, decomposed ammoniac, the metal being revivified and water and nitrogene produced.[64] The estimations of the composition of ammoniac that may be deduced from his experiments on the oxide of lead, differ very little from those already detailed.
II. Specific gravity of Ammoniac.
From the great solubility of ammoniac in water, it is difficult to ascertain its specific gravity in the same manner as that of a gas combinable to no great extent with that fluid. It is impossible to prevent the existence of a small quantity of solution of ammoniac in the mercurial airholder,[65] or apparatus containing the gas; and during the diminution of the pressure of the atmosphere on this solution,[66] a certain quantity of gas is liberated from it, and hence a source of error.
To ascertain, then, the weight of ammoniac, I employed an apparatus similar to that used for the absorption of nitrous gas by nitric acid.
50 cubic inches of gas were collected in the mercurial airholder, from the decomposition of muriate of ammoniac by lime; thermometer being 58°, and barometer 29,6.
100 grains of diluted sulphuric acid were introduced into the small graduated cylinder, which after being carefully weighed, was made to communicate with the airholder, the curved tube containing a small quantity of water. The gas was slowly passed into the fluid, and the globules wholly absorbed before they reached the top; much increase of temperature being consequent. When the absorption was compleat, the phial was increased in weight exactly 9 grains.
This experiment was repeated three times. The difference of weight, which was probably connected with alterations of temperature and pressure, never amounted to more than one sixth of a grain.
We may then conclude, that at temperature 58°, and atmospheric pressure 29,6, 100 cubic inches of ammoniac weigh 18 grains.
According to Kirwan, 100 cubic inches of alkaline air[67] weigh 18,16 grains; barometer 30°, thermometer 61. The difference between these estimations, the corrections for temperature and pressure being made, is trifling.
III. Of the quantities of true Ammoniac in Aqueous Ammoniacal Solutions, of different specific gravities.