appearance of a snowy white powder. This powder is ammonic chloride, and dissolved in water it has no effect upon either the red or blue litmus. 201. Ammonia gas is passed (a) into water, (b) into dilute sulphuric acid. Describe in detail what takes place. How can the gas be obtained from both these solutions? Jan. 1877. (a) If ammonia gas is passed into water, it forms a solution known under the various names of liquid ammonia, or ammonia spirits of hartshorn, liquor ammoniæ, or volatile alkali. To obtain from this solution the ammonia gas contained in it, it is sufficient to apply gentle heat to the liquid. (b) If ammonia gas is passed into dilute hydric sulphate it forms a neutral salt of ammonic sulphate, (NH4)2SO4. To obtain from this substance the ammonia contained in it, mix it with potassic hydrate or slaked or quick lime, then place it in a flask and heat it gently. The potassic hydrate acts as follows: 202. Give an account of the composition, preparation, and properties of the alkalies potash and soda. What compounds do these alkalies form when mixed with hydrochloric, sulphuric, and nitric acids? July 1847-July 1853. The alkalies potash and soda have for composition KHO, NаHO respectively. They are both prepared by decomposing the carbonate (K2CO, and Na2CO3) with calcic hydrate or slaked lime. Both are white substances, very deliquescent, and soluble in water. Their solution possesses in the highest degree the properties termed alkaline. It restores the blue colour to litmus paper which has been reddened by an acid, and neutralises the most powerful acids. Both dissolve skin and many other organic matters. Surgeons frequently use caustic potash as a cautery. Both, if exposed to the air, absorb the carbonic dioxide to form potassic carbonate (K2CO3) or sodic carbonate (Na2CO3); hence they should be kept in closely stopped bottles. Mixed with hydric chloride, potash forms potassic chloride (KCl), and soda forms sodic chloride (NaCl). Mixed with hydric sulphate, potash forms potassic sulphate (K2SO), and soda forms sodic sulphate (Na2SO) 4 Mixed with hydric nitrate, potash forms potassic nitrate (KNO3), and soda forms sodic nitrate (NaNO3). 203. How would you test an aqueous solution for hydric chloride (HCl), hydric sulphate (H2SO1), and ammonia (NH3) respectively? Jan. 1881. To test a solution of hydric chloride, I should pour into it a few drops of argentic nitrate, when a white precipitate is formed which is insoluble in hydric nitrate and soluble in ammonia. To test a solution of hydric sulphate, I should pour into the solution a few drops of baric chloride, when a K 130 CATECHISM OF MODERN ELEMENTARY CHEMISTRY. white precipitate is formed which is insoluble in hydric nitrate. Finally, to test a solution of ammonia, I should pour into the solution a few drops of potassic (KHO) or sodic hydrate (NaHO), and apply heat. The vapour that comes off renders moist red litmus paper blue. But the most delicate test of ammonia would be to mix it with lime and gently heat the mixture. A glass rod dipped in dilute hydric chloride and held over the mixture would cause the appearance of dense white fumes of ammonic chloride. |