106 SALTS OF SODA. 



in the arts of glass and soap-making, and other pro- 

 cesses where an alkali is employed. 



220. In order to obtain carbonate of soda by the 

 decomposition of common salt, it is first of all neces- 

 sary to convert the salt into a sulphate ; this is done 

 by mixing it in certain proportions with oil of vitriol 

 or sulphuric acid, and heating the mixture in a 

 furnace. Muriatic acid is expelled, and the sul- 

 phuric acid, which has a powerful attraction for the 

 soda, combines with it and forms sulphate of soda 

 (190). 



221. The second process is to mix the sulphate of 

 soda thus formed with chalk and pOunded coal, and 

 to strongly heat the mixture in a furnace ; the sul- 

 phate is decomposed at a high heat by the charcoal 

 or carbon of the coal, which takes oxygen both from 

 the sulphuric acid and from the soda, forming a sul- 

 phuret of sodium. This in turn is decomposed by the 

 chalk, and a carbonate of soda is produced, which is 

 of course impure, containing charcoal, and an in- 

 soluble compound of lime ; so that, by pouring water 

 on the crude salt after it is taken out of the furnace, 

 a clear colorless solution is procured, yielding on 

 evaporation a clean and nearly pure carbonate of 

 soda. 



222. This "soda "contains a large quantity of 

 water, although apparently dry ; and when left ex- 

 posed to the air, it does not, like the carbonate of 

 potash, attract water from the air, but, on the con- 

 trary, parts with it and becomes drier, at the same 



