Carbonate of soda is a colourless, inodorous salt ; it is devoid of smell, but has a disagreeable taste, though less so than carbonate of potaxli ; it is readily soluble in water. The primary form of this substance, when crystallised by moderate evaporation of the solution, is an oblique rhombic prism. The crystals are frequently very large. They contain about 62 per cent. of water, the greater part of which they lose by exposure to the air, and efflorescing, fall to powder. At high temperatures the salt becomes fluid and boils. Water at 60' dissolves half its weight of carbonate of soda, and boiling water con sidei-ably more. The solution possesses the alkaline property of turning vegetable yellows brown. Like other carbonates, this salt is decom posed by the stronger acids, with effervescence of carbonic acid ; and by lime, which separates its carbonic acid, it is rendered caustic.
The quantity of this salt prepared and used is enormous; it is required in making soap, and crown and plate glass, and for numerous other purposes.
2. Sesqui-cartionate of Soda (2Na0, 110, 3CO, + 3Aq.).—This com pound is found native in Hungary, and also near Fezzan in Africa. By the natives it is called 2'rona. lt is found in hard striated crystalline masses, is not altered by exposure to the air, and is readily soluble in water.
This salt appears to be formed when a solution of the carbonate of soda is heated with carbonate of ammonia, and probably also when a solution of the bi-carhonate is heated. Its taste is less alkaline than that of the carbonate, into which it is converted, when strongly heated, by losing ono-third of its carbonic acid.
Bicarbonate .1 Soda (Na0, HO, This salt may ho formed by passing carbonic acid gas into a solution of the carbonate of soda ; it is a crystalline granular compound. It is produced on the largo scale by exposing crystals of carbonate of soda to a current of carbonic acid gas.
Bicarbonate of soda has a very slightly alkaline taste, and acts very feebly on turmeric-paper. It requires about twelve times its weight of water for solution. \\lien the solution is boiled, it loses one-fourth of its carbonic acid, and is converted into aesqui-carbonate; at a red heat it loses all its water and half its carbonio acid, carbonate of soda result ing. It resembles the sesqui-carbonate in giving no precipitate with the salts of magnesia till heated ; and they both differ from the carbonate in this respect. It is used in medicine. Soda-water is, or at least should be, a solution of bi-carhonate of soda in water charged with carbonic acid gas under pressure. [AI:HATED WATERS.] Sulphate of Soda (Na0, SO, + 10Aq.), formerly called Marder'e salt, may be formed by the direct combination of the acid and alkali ; it is, however, generally prepared by decomposing common salt, as in the preparation of hydrochloric acid, or of carbonate of soda. It has
also been met with in nature, but not largely. [Semen, in NAT. HIST. Div.] This salt is readily soluble in water, and the solution by evaporation yields colourless transparent prismatic crystals, the primary form of which is an oblique rhombic prism. It has a very bitter taste; effloresces when exposed to the air, by losing water of crystallisation. Boiling water dissolves its own weight of this ealt, and water at 60° one-third of its weight. It is, however, most soluble at 93" Fehr.; at will that temperature 100 parts of water wi dissolve 50.6 parts of the salt. A boiling saturated solution of sulphate of soda may be cooled and kept for months without any crystals forming in it, provided that air be excluded; let, however, a crystal of the sulphate, or any solid matter, even a particle of dust, be dropped into the liquid, and the whole then shoots into crystals with considerable elevation of tempera ture. Sulphate of soda is insoluble in alcohol. When exposed to heat it first undergoes watery fusion, by melting in its water of crystallisation ; when the water has been expelled, it becomes opaque white, and at a red heat it melts.
An anhydrous sulphate of soda, and a hydrate containing Na0, SO, + 7Aq. may also be obtained. Bisulphate of soda contains NaO, HO, Sulphite of Soda (NaO, SO, + 7Aq.) is formed on passing sulphurous acid gas over carbonate of soda. It is used by paper manufacturers, under the name of antichlor, for removing the last trace of chlorine from their rag-pulp. Pisulphite of soda contains Na0, 110, 250,.
Silicates of Soda. [SILICON; Gratss.] Acetate of Soda. [ACETATE.] Phosphoric Acid combines with soda to form several compounds. [PnosrlIORus.] Borate of Soda is a compound of boracic acid and soda. [BORON.] For an account of numerous other salts of soda we must refer to chemical treatises ; those whose properties we have detailed being merely the most useful.
General l'ropertios of the Salts of Sodium.—Unliko the salts of potash, there is no acid nor any metallic oxide which forms a perfectly insoluble compound with the salts of soda, so that they cannot be precipitated in combination from solution. The best mode of dis tinguishing between these two alkalies is, by the yellow corour which soda salts communicate to the blow-pipe flame, salts of potash giving a violet tinge. They are separated from each other by taking advantage of the insolubility of the double chloride of platinum and potassium, and the great solubility of the corresponding sodium salt.