Hence it was evident that some of the salt had been lost during the evaporation.
To find the quantity lost, fibrous nitrate of ammoniac was dissolved in small quantities in the solution, the specific gravity of which was examined after every addition of 3 grains. When 16 grains had been added to it, it became of 1,15.
Consequently, the solution composed of 200 grains of ammoniacal, and of 385,5 of nitric acid solution, contained 262 grains of salt of fibrous crystalization, and of this salt 8 grains were lost during the evaporation.
But the alkali in 200 grains of ammoniacal solution of,9056 = 50,5 grains. And the true nitric acid in 385,5 grains of solution of 1,306 = 190 grains.
Then 262-240,5 = 21,5, the quantity of water.
And 262 grains of fibrous crystalized nitrate of ammoniac, contain 190 grains true acid, 50,5 ammoniac, and 21,5 water. And 100 parts contain 72,5 acid. 19,3 ammoniac, and 8,2 water.
In proportion as the temperature employed for the evaporation of nitro-ammoniacal solutions, is above or below 212°, so in proportion does the salt produced contain more or less water than the fibrous nitrate. But whatever may have been the temperature of evaporation, the acid and alkali appear always to be in the same proportions to each other.
Of the salts containing different quantities of water, two varieties must be particularly noticed. The prismatic nitrate of ammoniac, produced at the common temperatures of the atmosphere, and containing its full quantity of water of crystalisation; and the compact nitrate of ammoniac, either amorphous, or composed of delicately needled crystals, formed at 300°, and containing but little more water than exists in nitric acid and ammoniac.
To discover the composition of the prismatic nitrate of ammoniac, 200 grains of fibrous salt were dissolved in the smallest possible quantity of water, and evaporated in a temperature not exceeding 70°. The greater part of the salt was composed of perfectly formed tetrahædral prisms, terminated by tetrahædral pyramids. It had gained in weight about 8,5 grains.
Consequently 100 grains of prismatic nitrate of ammoniac may be supposed to contain 69,5 acid, 18,4 ammoniac, and 12,1 water.