SODIt'M 515 



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 this 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 490). Even up to the present time this process is 

 -carried on in Normandy. In Prance, 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 



which separate are raked out and placed on planks, where the liquid flows off. Caustic 

 .soda remains in the residue, and also any sodium chloride which was not decomposed in 

 the foregoing process. 



Part of the sodium carbonate is crystallised in order to purify it more thoroughly. In 

 -order to do this a saturated solution is left to crystallise at a temperature below 30 in a 

 current of air, in order to promote the separation of the vapour of water. Then the large 

 transparent crystals (efflorescent in air) of Na 2 CO 5 ,10H.2O are formed which have been 

 .spoken of already (Chapter I.). 



13 Among the drawbacks of the Leblanc process are the accumulation of ' soda waste,' 

 .and the impossibility at the comparatively low price of sulphur (especially in the form of 

 pyrites) of finding a suitable employment for it (although this waste can furnish sulphur 

 and sulphur compounds, for which purposes it is sometimes treated), and also the insuffi- 

 -cient purity of the sodium carbonate for many purposes. The advantage of the Leblanc 

 ^process, besides its simplicity and cheapness, are that almost all acids having a commercial 

 value are obtained as bye-products ; chlorine and bleaching powder are produced with 

 4ihe assistance of the large amount of hydrochloric acid which appears as a bye-product, 

 -and caustic soda is very easily made, and the demand for it increases every year. In 

 those places where salt, pyrites, charcoal, and limestone (which are the materials required 

 .for soda works) are found side by side as, for instance, in the Ural or Don districts all 

 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 various methods of manufacturing soda 

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

 ^decomposed by oxide of lead, PbO, forming lead chloride and sodium oxide, which, with car- 

 bonic 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, Na 6 Fe 4 S 3 , is formed, which is insoluble in water and 

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

 sulphide; this when roasted can give sulphurous anhydride, which is indispensable 

 -for the manufacture of sulphuric acid, and ferric oxide, which is again used in the 



L L 2 



