Sulphate of Sodium. (FR., Sulfate de &ode ; GER., Schwefelsaures Aaron.) Formula, Synonyms, Glauber's salts, salt cake.—Sulphate of sodium was discovered about the year 1658, by Glauber. It occurs in nature in certain mineral waters—e. g. at Cheltenham—and in the minerals mirabilite and glauberite. The former is found in Spain, Hungary, Switzerland, Austria, and many other countries, also in lava, and as an efflorescence upon the Caspian steppes. Glanberite is a mixture of crystallized sulphate with gypsum, and occurs in Spain, Bavaria, Chili, Ste.
Sulphate of sodium when pure, esystallizes in right rhombic prisms, with either 8 or 10 equivalents of water. The crystals effloresce in the air, and lose water. Heated, the salt fuses into a white solid, again becoming liquid at a red heat. The crystals are soluble in twice their own weight of cold water at the solubility rapidly increasing with an increase of tempe rature up to 33°. At that point, 100 parts of water dissolve 117.9 parts of the salt, corresponding to 52 parts of anhydrous sulphate. Beyond 33°, the solubility decreases, and a portion of sulphate is deposited. At water dissolves its own weight of the salt, It is insoluble in alcohol.
Sodium sulphate is a bye-product in many. chemical operations—in the preparation of nitric acid, sal-ammoniac and magnesium carbonate ; also in the slags from various glass processes. Its production by the action of sulphuric acid upon chloride of sodium, has already been set forth. Pure sulphate may be prepared in this way from pure materials, any excess of sulphuric acid being neutralized by carbonate of sodium, after dissolving the sulphate in water. The solution is then filtered, concentrated, and crystallized. A pure salt is also obtained from the evaporation of sea-water, in the process of Balard and Merle described when treating of potassium chloride. The magnesium sulphate and sodium chloride at a low temperature react upon one another, and produce magnesium chloride, which remains in solution, and sodium sulphate which crystallizes out. The bye-product obtained from the nitric acid and hydrochloric acid processes, called respectively "nitre cake," and "salt cake," is of very poor quality, containing large amounts of either free acid or free salt. A good Glauber's salt is produced from the "pan scales" of salt works, by separating the sodium sulphate from the gypsum with hot water. The solution is con centrated and run into shallow coolers of wood lined with lead. As soon as the liquors are cool a rod is drawn along the vessel. This causes small single crystals to separate out which afterwards grow into masses of fine needle-shaped prisms. The liquor is kept shallow to prevent the formation of too large crystals. On the other hand any violent agitation causes very small crystals to separate
out —" flour" as they are termed. When the liquors are cold, the mothers are siphoned off, the crystals washed with cold water, and dried at a very gentle heat.
Besides the enormous consumption of sulphate of sodium in the alkali manufacture, the salt is used in the production of various kinds of glass—chiefly bottles ; in certain medicinal preparations ; and, to some small extent, in dyeing and printing, to fix lead mordants preparatory to dyeing them orange or yellow.
Tangstates of Sodium.—Several of these salts are well known, but only two possess any interest to the general reader—the neutral salt, NO, and an acid salt, The latter is prepared by fusing the neutral salt with tungstic oxide, and boiling the product with water ; or by fusing wolfram with one-third its weight of sodium carbonate. It forms large prismatic crystals, specific gravity containing 16 atoms of water of crystallization, and with a bitter saline taste. The crystals effloresce in dry air, giving off nearly all the water of crystallization and being con verted into the anhydrous salt. It melts at a red heat and is readily soluble in water.
The neutral salt is the tungstate commonly used. With two atoms of water, it crystallizes in colourless transparent rhombic tables, which have an alkaline reaction and bitter taste. The crystals do not effloresce, are soluble in 4 parts of cold water and half the quantity of hot, and in soluble in alcohol. At a red heat, the water of crystallization is given off and a fused mass of the anhydrous salt is obtained forming a colourless liquid, which assumes a crystalline appearance when cold.
Upon a fairly large scale, the neutral tungstate is produced from au ore of tungsten, called wolfram, found in considerable quantities in Cornwall, usually associated with tin ores. The mineral, a native tungstate of iron and manganese, is mixed with sodium carbonate, or salt cake, and thrown into a reverberatory furnace. The proportions vary considerably with the amount of wolfram present in the stone operated upon, which must be ascertained by actual analysis. The mixture is then regulated according to the chemical equivalents, about 10 cwt. forming an ordivary charge for the furnace. The batch is worked thoroughly after the manner of a sulphate furnace, soluble tungstate of soda, tin and manganese oxides, and silica being produced. When the charge is cooled, it is broken up and lixiviated with water in small wooden vats. Tungstate of soda is dissolved, drawn 4 concentrated in iron pans, and crystallized.