Sulphates, salts formed by the union of sulphuric acid with bases. The union, strictly speaking, is only partial, as a portion, and in normal salts all, of the hydrogen of the sulphuric acid is displaced by the basyle. (See Salts.) Thus, H2S04 + 2K = 2H + K2S04, normal sulphate of potassium; or H2S04 + K = H + KHSO4, acid sulphate of potassium. The sulphates are extensively employed in the arts, in medicine, in agriculture, and in the chemical laboratory. 1. Sulphates of Alumina. The normal sulphate, A123S03 + 18H20, is found native in many localities, as on the volcanic island of Milo in the Grecian archipelago, in the craters of volcanoes in the Andes, and at Adelaide in Australia. It is known in mineralogy as alunogen, hair salt, feather alum, and halotrichite. Its hardness is 1.5 to 2; sp. gr. 1.6 to 1.8; lustre vitreous; color white, or tinged with yellow or red. It is manufactured in large quantities, is known in commerce as concentrated alum, and is used in dyeing instead of common alum. Clay as free as possible from iron is heated to redness, and then ground and mixed with half its weight of sulphuric acid of sp. gr. 1.45, in a reverberatory furnace, till the acid begins to volatilize.
After exposure to the air for several days, water is added and the solution freed from what iron it may contain by precipitation with fer-rocyanide of potassium. The solution is then evaporated to a sirup, which solidifies on cooling. It is soluble in two parts of water, insoluble in alcohol. There is a series of double aluminic sulphates, forming true alums, which are treated under the head of Alum. Not all alums contain aluminum, but they are so named because they are formed on the type of the alum salts. 2. Sulphates of Barium. Some of the sulphates of barium are double salts. The most important is the neutral sulphate, BaS04, or heavy spar, which is found native in largo quantities, and when ground into powder is used to adulterate white lead as a pigment. An amorphous sulphate is made on a large scale for the same purpose, and called permanent white. There is an acid salt, BaH22S04, and a basic soda sulphate, Ba-N22S04. 3. Sulphates of Calcium and Chromium. An anhydrous neutral sulphate of calcium, CaS04, occurs native as the mineral anhydrite. It may be formed artificially in crystals by fusing sulphate of potash with an excess of chloride of calcium.
Gypsum is native hy-drated sulphate of calcium, CaS042H20. (See Gypsum.) The sulphates of chromium, both the pure chromium and also the double salts, are an important class of compounds, and include the chrome alums, as ammonio-chrome alum, potassio-chrome alum, and sodio-chrome alum. 4. Sulphates of Copper. The normal sulphate, CuSO4 + 5H2O, is the blue vitriol of commerce, extensively used in the arts. (See Copper, vol. v., pp. 318-'19.) There are several basic sulphates of copper, and double sulphates of copper and ammonia of various shades of blue, some of which form solutions of exceeding beauty. By mixing solutions of ammonio-cupric sulphates or of potassio-cupric sulphates with corresponding double sulphates of cobalt, iron, magnesium, manganese, nickel, or zinc, an interesting series of complex salts is obtained, all of which crystallize in monoclinic prisms and tables, isomorphous with the magnesium double salts; and furthermore, by mixing the solutions of three or four of these double salts, others still more complex may be formed, isomorphous with the preceding. Copper also forms with magnesium, sodium, and zinc beautiful double sulphates.
In the preparation of cupric sulphate from materials which contain iron compounds, several so-called ferroso-cupric sulphates are formed, having different proportions of base, but which are not true double salts. The Salzburg vitriol, prepared at Buxweiler in Alsace, contains 3 molecules of iron to 1 of copper;. Ad-mont vitriol, 5 to 1; Baireuth vitriol, 7 to 1. 5. Sulphates of Iron. Sulphuric acid forms with iron an extensive series of salts, some of which have a constitution analogous to the peroxide, and are called ferric salts; others, analogous to the protoxide, are called ferrous salts. Among the former are several interesting double salts, including ammonio-ferric sulphate, or ammonia-iron alum, and potassio-ferric sulphate, or potash-iron alum. Ferrous sulphate, green vitriol, or copperas, FeS04 + 7H20 (or FeOS03 + 7H0, old formula), is the most important commercial salt of iron. It occurs native, sometimes in crystals, but more often in amorphous masses, in iron mines in various parts of the world, being formed by the oxidation of iron pyrites; but most of the copperas consumed in the arts is prepared simultaneously with alum from schists containing iron pyrites.
Ferrous sulphate crystallizes in mono-clinic prisms or tables, which when moist readily absorb oxygen and pass into ferric sulphate; but if crushed and deprived of moisture by strong pressure between folds of cotton cloth or filter paper, it may be kept in bottles for a long time without change. (See Copperas.) G. Other Metallic Sulphates. The normal sulphate of magnesium, MgS04 + 7H20, is described under the title Epsom Salt.^ There is an acid sulphate and several double salts. The sulphates of potassium are described with that metal. Glauber's salt is the normal and principal sulphate of sodium. (See Glauber's Salt.) The other metallic sulphates of sufficient importance are treated under the heads of the respective metals. 7. Alcoholic Sulphates. Sulphuric acid combines with various alcohol radicals to form a series of 'sulphuric ethers, the most important among which are acid sulphate of ethyle, or sulphovinic acid, (C2H5)HS04, and neutral sulphate of ethyle, or true sulphuric ether, (C2H5)2S04. (This latter ether must be distinguished from what is ordinarily called sulphuric ether, which is the oxide and not the sulphate of the radical ethyle, C2H5.) Sulphovinic acid is formed by the action of strong sulphuric acid upon alcohol, ether, or ethylene, and was first noticed by Da-bil in 1800 in the residues of the preparation of common ether.
The molecule of hydrogen which it contains may be replaced by a metal forming a salt which is called a sulphovinate, or ethyle sulphate. Neutral sulphate of ethyle, or true sulphuric ether, is formed by passing sulphuric anhydride into a flask containing common sulphuric ether surrounded by a freezing mixture. It is a yellowish oily liquid of sp. gr. 1.12, having a sharp taste and the odor of oil of peppermint. As it is decomposed when heated in the air, it must be distilled in an atmosphere of carbonic anhydride. Sulphuric acid forms with methyle an acid sulphate of methyle, or sulpho-methylic acid, CH3HS04, and a neutral sulphate of methyle or methylsulphuric ether, (CH3)3S04. The molecule of hydrogen in sulpho-methylic acid may be replaced by a metal, forming a salt called a methyl-sulphate.