SODA MANUFACTURE. This branch of manufacturing chemistry is a very interesting one as exemplifying the important advantages which we derive from our inexhaustible stores of salt, and from the numerous useful substan ces which this salt is made to yield.
What is usually called soda is not strictly such ; it is Carbonate of Soda; but both are produced from common salt. Sulphuric acid is the agent which enables salt to yield these valuable products. In some of the chemical works at Glasgow and Newcastle, sulphuric acid is made by the aid of sulphur ; and this acid and salt are used for further processes. When a high excise duty was laid upon common salt, soda was made from kelp and barilla; but now that salt is purchaseable at so low a price, all our soda is obtained from this source, for employment in soap making, alum making, bleaching, washing, &c.
In, manufacturing soda a given weight of salt is placed in a reverberatory furnace, in a leaden pan, and sulphuric acid is dropped down upon it through a leaden pipe brought through the roof of the furnace. The salt liquifies in the acid, and a gaseous vapour ascends ; this vapour is hluriatic acid gas, which takes away the chlorine from the salt, and which is condensed into a liquid in the way described in a former article [MouLiTro Acre.] The sulphuric acid forms pasty mass
of sulphate of soda, with the remaining ingre clients in the furnace. The sulphate is taken from the furnace, mixed with fine lime and fire coal, put into another furnace, and heated. The coal kindles, and melts the sulphate and lime into a viscid mass, which after being repeatedly raked and stirred, is removed from the furnace into iron trays. The mass, which is called ball soda, crude soda, or British barilla, is a mixture of carbonate of soda with sulphuret of calcium. The carbonate is sepa rated from the sulphuret by steeping in water, which dissolves the former but not the latter ; there is formed, in fact, a solution of carbonate of soda, which, in being evaporated, yields the solid carbonate almost entirely from sulphur. This is a yellowish earthy substance, called soda ash or soda salt, largely used in manu factures. But a more pure and crystallised carbonate is required for some purposes ; this is producedby dissolving, settling, evaporating, ancLcrystallismg, whereby beautiful crystals of carbonate of soda are produced. By a further chemical process the carbonic acid is driven off, and pure or caustic soda results..