SODIUM 



The above-mentioned process for making soda was discovered in the 

 year 1808 by the French doctor Leblanc, and is known as the Leblanc 

 process. The particulars of the discovery are somewhat remarkable. 

 Sodium carbonate, having a considerable application in industry, was 

 for a long time prepared exclusively from the ash of marine plants 

 (Chapter XI., page 497). Even up to the present time this process is 

 carried on in Normandy. In France, where for a long time the manu- 

 facture of large quantities of soap (so-called Marseilles soap) and various 

 fabrics required a large amount of soda, the quantity prepared at the 

 coast was insufficient to meet the demand. For this reason during 

 the wars at the beginning of the century, when the import of foreign 

 goods into France was interdicted, the want of sodium carbonate was felt. 

 The French Academy offered a prize for the discovery of a profitable 

 method of preparing it from common salt. Leblanc then proposed the 

 above-mentioned process, which is remarkable for its great simplicity. 15 



solution of magnesium chloride obtained is again used, and the washed calcium sulphite 

 is brought into contact at a low temperature with hydrochloric acid (a weak aqueoua 

 solution) and hydrogen sulphide, the whole of the sulphur then separating: 



CaSO 3 + 2H 2 S+2HC1 = CaCl 2 + 3H 2 O + 83. 



But most efforts have been directed towards avoiding the formation of soda 

 waste. 



15 Among the drawbacks of the Leblanc process are the accumulation of 'soda 

 waste ' (Note 14) owing to the impossibility at the comparatively low price of sulphur 

 (especially in the form of pyrites) of finding employment for the sulphur and sulphur 

 compounds for which this waste is sometimes treated, and also the insufficient purity 

 of the sodium carbonate for many purposes. The advantages of the Leblanc process, 

 besides its simplicity and cheapness, are that almost the whole of the acids obtained 

 as bye-products have a commercial value; for chlorine and bleaching powder are 

 produced from the large amount of hydrochloric acid which appears as a bye-product ; 

 caustic soda also is very easily made, and the demand for it increases every year, 

 In those places' where salt, pyrites, charcoal, and limestone (the materials required 

 for alkali works) are found side by side as, for instance, in the Ural or Don 

 districts conditions are favourable to the development of the manufacture of sodium 

 carbonate on an enormous scale ; and where, as in the Caucasus, sodium sulphate 

 occurs naturally, the conditions are still more favourable. A large amount, however? 

 of the latter salt, even from soda works, is used in making glass. The most important 

 soda works, as regards the quantity of products obtained from them, are the English 

 works. 



As an example of the other numerous and varied methods of manufacturing soda 

 from sodium chloride, the following may be mentioned : Sodium chloride is decom- 

 posed by oxide of lead, PbO, forming lead chloride and sodium oxide, which, with carbonic- 

 anhydride, yields sodium carbonate (Scheele's process). In Cornu's method sodium 

 chloride is treated with lime, and then exposed to the air, when it yields a small 

 quantity of sodium carbonate. In E. Kopp's process sodium sulphate (125 parts) is mixed 

 with oxide of iron (80 parts) and charcoal (55 parts), and the mixture is heated in reverbe- 

 ratory furnaces. Here a compound, Na6Fe 4 S 3 , is formed, which is insoluble in water> 

 absorbs oxygen and carbonic anhydride, and then forms sodium carbonate and ferrous 

 sulphide ; this when roasted gives sulphurous anhydride, the indispensable material 



