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. To ascertain the composition of the compact nitrate of ammoniac, I exposed in a deep porcelain cup, 400 grains of the fibrous salt, in a temperature below 300°. It quickly became fluid, and slowly gave out its water without any ebullition, or liberation of gas. When it was become perfectly dry, it had lost 33 grains. I suspected, that in this experiment some of the salt had been carried off with the water; to determine this, I introduced into a small glass retort, 460 grains of fibrous salt; it was kept at a heat below 320°, in communication with a mercurial apparatus, in a regulated air-furnace, till it was perfectly dry: it had lost 23 grains. No gas, except the common air of the retort came over, and the fluid collected had but a faint taste of nitrate of ammoniac. Though in this experiment I had removed all the fluid retained in the neck of the retort, still a few drops remained in the head, and on the sides, which I could not obtain. It was of importance to me to be accurately acquainted with the composition of the compact salt, and for that reason I compared these analytical experiments with a synthetical one. I saturated 200 grains of solution of ammoniac, of,9056 with acid, ascertained the specific gravity of the solution, evaporated it at 212°, and fused and dried it at about 300°-260°. It gave 246 grains of salt, and a solution made of the same specific gravity as that evaporated, indicated a loss of 9 grains. Consequently, 255 grains of this salt contain 50,5 grains alkali, 100 grains acid, and 14,5 grains water. We may then conclude, that 100 parts of compact nitrate of ammoniac contain 74,5 acid, 19,8 alkali, and 5,7 water. V. _Decomposition of Carbonate of Ammoniac by Nitric Acid._