SODA, MANUFACTURE OF. Soda, or, more correctly, carbonate of soda, occupies the chief place among our leading chemical manufactures, alike from its own importance, and also on account of its influence ou other great chemical industries, such as glass making, soap-making, bleaching, etc. • A native carbonate of soda, or rather a sesqui-carbonate, called natron (q.v.), is found in Egypt and some other parts of the world. In Hungary, several manufactories exist for the paritIcation of a native soda found there. Formerly, most of the soda in use was extracted from certain plants; and two kinds were known in commerce under the names of barilla (q.v.), and kelp (q.v.).
But the quantity of soda got from all other sources is now insignificant in comparison with that manufactured from common salt (chloride of sodinm—see Sornum), The pro cess was invented by a Frenchman named Leblanc, and was first made known to the world by a commission of the French republic in 1794, although dating some years earlier. It is unquestionably the most valuable discovery in the entire range of chemical manufactures; and it has been practiced for nearly ninety years without any important alteration. It is sad to think that the author of this invention reaped no betaeffi from it himself, but spent the list of his days in an hospital, " aitvreck in fortune, health, and hope." Owing partly to the war between France and England, and partly also to the existence of a duty of £80 per ton on common salt, which continued for eight years after the close of the war, Leblanc's process was not adopted in Great Britain except on a very limited scale till 1823. After the repeal of the tax in that year, Mr. James Muspratt erected his celebrated works at Liverpool, adopted the process in its entirety, and succeeded, after overcoming many difficulties, in establishing in Great Britain a chemical manufacture which has since become the most important in the world, and for which nearly 600,000 tons of common salt are now annually required.
The object of the soda-process is to separate the sodium of the salt, and unite it with oxygen to form caustic soda, or, what is more generally done, to unite the sodium with both oxygen and carbonic acid to form carbonate of soda. The several stages of the
process are as follows: Firvt Operation—The Protiaclion of S'alphafe of Soda.—The decomposition of the com mon salt is effected by treating it with sulphuric acid, which transforms it into sulphate of soda and hydrochloric acid. This operation was long conducted in a common reverbera tory furnace (q.v.). and the hydrochloric acid was suffered to escape into the air. Not only was the acid thus lost. hut it destroyed all vegetation in the neighborhood of soda works, and involved their owners in serious law-suits for damages. The great chimneys of the St. Hollox works, Glasgow. and Mr. Muspratt's, Liverpool. which are nearly 500 ft. high, were erected with a view of miring this evil, but they were found to be ineffectual. The most improved furnaces now in use for the purpose are built in pairs, and in the front part of each there is a shallow cast-iron pan, nine ft. in diameter, with a sheet-iron cover, and so built that the tire may act on the bottoms and sides. Behind this, an oblong brick chamber, 30 ft. by 9 ft., is situated, with separate fire-places, and called the salt-cake furnace. Acid flues are led from each compartment of the double furnace into one main flue, which has its outlet into a condensing tower, to be presently described. Separate flues arc also provided for the conveyance of smoke to a main chimney. The furnace is worked in the following way: when it is properly heated, salt to the amount of 10 cwts. is thrown in by an opening, and about 80 gallons of strong sulphuric acid are heated and run in. The mixture, which is well stirred with an iron rake, gradually thickens, and in about an hour the pasty mass, not yet all decomposed, is pushed through the opening into the salt-cake chamber. Here it is spread out on the sole, and maintained at a red heat for another hour, when the whole of the hydrochloric acid is expelled, and the conversion into sulphate of soda complete. A pair of furnaces, about one-half larger than those above described, will produce about 19 tons of sulphate of soda in a day, for which 16 tons of common salt are required. At the St. Rollox chemical works, Glasgow, about 500 tons of common salt are decomposed weekly.