454 SULPHATES bydrite. It may be formed artificially in crys- tals by fusing sulphate of potash with an excess of chloride of calcium. Gypsum is native hy- drated sulphate of calcium, CaS0 4 2H 2 O. (See GYPSDM.) The sulphates of chromium, both the pure chromium and also the double salts, are an important class of compounds, and in- clude the chrome alums, as ammonio-chrome alum, potassio-chrome alum, and sodio-chrome alum. 4. Sulphates of Copper. The normal sulphate, CuS0 4 + 5H 2 O, is the blue vitriol of commerce, extensively used in the arts. (See COPPER, vol. v., pp. 318-'i9.) 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 exceed- ing 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 ob- tained, all of which crystallize in monoclinic prisms and tables, isomorphous with the mag- nesium double salts ; and furthermore, by mix- ing 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, hav- ing different proportions of base, but which are not true double salts. The Salzburg vit- riol, prepared at Buxweiler in Alsace, con- tains 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 per- oxide, and are called ferric salts ; others, anal- ogous to the protoxide, are called ferrous salts. Among the former are several interesting dou- ble salts, including ammonio-ferric sulphate, or ammonia-iron alum, and potassio-ferric sul- phate, or potash-iron alum. Ferrous sulphate, green vitriol, or copperas, FeSO 4 + 7H 2 O (or FeOSOs + 7HO, old formula), is the most im- portant 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 oxida- tion of iron pyrites ; but most of the copperas consumed in the arts is prepared simultaneous- ly with alum from schists containing iron py- rites. Ferrous sulphate crystallizes in mono- clinic prisms or tables, which when moist read- ily 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.) 6. Other Metallic Sulphates. The normal sul- phate of magnesium, MgS0 4 + 7II 2 0, is de- scribed under the title EPSOM SALT. There is an acid sulphate and several double salts. The SULPHIDES sulphates of potassium are described with that metal. Glauber's salt is the normal and prin- cipal sulphate of sodium. (See GLAUBER'S SALT.) The other metallic sulphates of suffi- cient importance are treated under the heads of the respective metals. 7. Alcoholic Sul- phates. 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, (C 2 H B )HS0 4 , and neutral sulphate of ethyle, or true sulphuric ether, (C S H 6 ) 2 S0 4 . (This latter ether must be distinguished from what is ordi- narily called sulphuric ether, which is the oxide and not the sulphate of the radical ethyle, CaHs.) 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 freez- ing 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. Sul- phuric acid forms with methyle an acid sul- phate of methyle, or sulpho-methylic acid, CH 3 HS0 4 , and a neutral sulphate of methyle or methylsulphuric ether, (CH S )3S0 4 . The molecule of hydrogen in sulpho-methylic acid may be replaced by a metal, forming a salt called a methyl-sulphate. SULPHIDES, or Sulphnrets, compounds in which sulphur forms the electro-negative element. Sulphur unites with all the metals, with most of the non-metallic elements, and with many organic radicals. The sulphides have generally a constitution corresponding to the oxides, and like them may be divided into acid and basic sulphides, which are capable of uniting and forming sulphur salts. Thus, we have stan- nate of potassium, K 2 SnO s , and also sulpho- stannate of potassium, KaSnSs. The sulphides are decomposed more or less perfectly by hy- drochloric acid, and behave like the correspond- ing oxides, yielding one molecule of sulphy- dric acid for every molecule of sulphur in the sulphide. Thus, FeS + 2HCl=H 2 S + FeCl 2 ; and SbSs + 6HC1=3H 2 S + 2SbCl,. Of the sul- phides of the non-metallic elements, those of carbon and chlorine are the most important. Bisulphide of carbon, carbon disulphide, or sulpho-carbonic acid, CS 2 , is the only sulphide of carbon which is positively known. It is prepared on a large scale as a solvent for vari- ous manufacturing purposes. A large earthen retort has a tube which passes through the mouth down to near the bottom. The retort is filled with charcoal and heated to redness in a furnace, and bits of sulphur are dropped from
