Iodide of Zinc (ZnI) is readily obtained by heating iodine and zinc together in water ; the solution, when perfect, is colourless, and is to be evaporated in a retort, and when the water is entirely separated, the iodide of zinc fuses and volatilises in fine prismatic crystals. By exposure to the air this iodide is decomposed, the metal being oxidised, and the iodine set free.
Sulphide of Zinc (ZnS).—This compound, which exists plentifully in nature, is obtained artificially with considerable difficulty, and by the direct action of its elements is perhaps scarcely possible •, but when oxide of zinc is heated with sulphur in excess, a yellow brown eulphuret of the metal is obtained ; when also sulphuret of potassium is added to a solution of a salt of zinc, a white hydrate of the sulphide of zinc is precipitated.
Phosphide of Zinc is procured by strongly heating in a retort a mixture of six parts of oxide of zinc, nix parts of phosphoric acid, and one part of powdered charcoal ; a sublimed mass is obtained, which is of a silvery-white colour, metallic lustre, and vitreous fracture. Its composition has not been determined.
Selenide of Zinc.—If the vapour of selenium be passed over zinc heated to redness, the mass takes fire and explodes, and the exterior of the vessel is covered with a lemon-yellow powdery substance, which is selenide of zinc ; this is partially soluble in nitric acid with the evolution of nitric oxide; and a red powder is deposited, which is however finally dissolved.
We shall now briefly describe some of the oxisalts of zinc, or eiose consisting of acids combined with oxide of zinc.
1P7trate of Zinc VziONO, 6H0).—Th:s salt is readily obtained by the action of the acid upon the oxide of the metal, or upon the meta: itself ; in the latter case nitric: or nitrous oxide is produced according to the degree of concentration of the acid.
The solution of nitrate of zinc is colourless, and by due evaporation it yields colourless crystals, which are deliquescent ; very soluble in water and in alcohol : they are decomposed by ignited charcoal, and impart to it a greenish-blue flame.
Sulphate of Zinc (ZnOSO„ + 7H0).—This, which is the salt of zinc most extensively employed both in medicine and the arts, may be prepared by dissolving the oxide of the metal in dilute sulphuric acid ; but it is always procured by acting on the metal itself, which it oxidised by the decomposition of water, with the oxygen of which it combines and evolves the hydrogen. The solution is colourless, and by evaporation readily yields crystals, which are usually small, and the primary form of which is a right rhombic prism. Sulphate of zinc
has a disagreeable metallic taste ; it is not altered by exposure to the air, but if moderately heated loses its water of cryatallisstion, and when subjected to a high temperature is entirely decomposed, the acid being expelled, the oxide only remaining. This salt is very soluble in water at GO°, and much more so iu boiling water. There is an impure sulphate of zinc used in the arts, under the name of white vitriol ; it is a colourless granular mass, obtained by the oxidisement of the native sulphide of zinc or blonde.
Carbonate of Zinc (2 Zu0 CO, + 3 Zn 0 HO). —Metallic zinc and hydrated oxide of zinc are both dissolved by an aqueous solution of carbonic acid ; but the nature of the carbonate formed, when the excess of carbonic acid is expelled by spontaneous evaporation, has not been ascertained. When an alkaline carbonate is added to a solution of a salt of zinc, a white precipitate is obtained, which is the above compound of carbonate and hydrate of zinc, and not a simple carbonate.
of Zinc 3110) is prepared by dissolving either the metal or its oxide in the acid, or by decomposing sulphate of zinc by acetate of lead. The solution is colourless, and yields thin rhombic plates, which are not deliquescent, but are very soluble in water. It is occasionally employed in medicine.
Characters of the Salts of Zinc.—They are usually soluble in water, colourless, have an unpleasant metallic taste ; the alkalies ammonia, potash, and soda decompose them, precipitating a colourless hydrate, which is soluble in excess of these precipitants. The alkaline car bonates also decompose the salts of zinc, but the carbonate of ammonia only, when added in excess, redissolves the carbonate thrown down in any notable quantity. Hydrosulphuric acid decomposes neutral, but not acid or alkaline solutions of zinc; the precipitate obtained is a hydrated sulphide of zinc. Tincture of galls gives no precipitate, and ferrocyanide of potassium a white one with the salts of zinc.
Alloys of Zinc.—Potassium and sodium form with zinc brittle alloys, decomposable by exposure to air and moisture. With copper it com bines to form brass, and with iron it yields a very hard alloy, which is very energetically acted upon by sulphuric acid. If plates of hot iron be dipped into melted zinc, they acquire the appearance of tin-plate, and the iron is prevented from rusting. Such coated iron is termed galvanised iron.
Sheet-zinc is now largely employed for covering buildings. Platen of this metal are also used in the construction of voltaic batteries.