SODir.M 511 



may be obtained, Na 2 SO 4 + BaX., = 1 JaS< > , + - NaX. Barium sulphate 

 thus formed, being a very sparingly-soluble salt, is obtained as a pre- 

 cipitate, whilst the sodium hydroxide, or salt, NaX, is obtained in 

 solution, because all salts of sodium are soluble. Berthollet's doctrine 

 permits all such cases to be foreseen. 



The reactions of decomposition of sodium sulphate are above all 

 noticeable by the separation of oxygen. Sodium sulphate itself is very 

 stable, and it is only at a temperature sufficient to melt iron that it is 

 possible to separate the elements SO 3 from it, and then only partially. 

 However, the oxygen may be separated from sodium sulphate, as from 

 all other sulphates, by means of many substances which are able to 

 combine with oxygen, such as charcoal and sulphur, but hydrogen is 

 not able to produce this action. If sodium sulphate be heated with 

 charcoal, then carbonic oxide and anhydride are evolved, and there is 

 produced, according to the circumstances, either the lower oxygen 

 compound, sodium sulphite, Na 2 SO 3 (for instance, in the formation 

 of glass) ; or else the decomposition proceeds further and sodium 

 sulphide, Na 2 S, is formed, according to the equation Na 2 SO 4 + 20 

 = 2CO 2 + Na 2 S. 



On the basis of this reaction the greater part of the sulphate of 

 sodium prepared at chemical works is converted into soda ash that is, 

 sodium carbonate, Na 2 CO 3 , which is used for many purposes. In the 

 form of carbonates, the metallic oxides behave in many cases just as 

 they do in the state of oxides or hydroxides, owing to the feeble acid 

 properties of carbonic acid. However, the majority of the salts of 

 carbonic acid are insoluble, whilst sodium carbonate is one of the few 

 soluble salts of this acid, and therefore reacts with facility. Therefore 

 sodium carbonate is employed for many purposes, in which it acts owing 

 to its alkaline properties. Thus sodium carbonate, even under the action 

 of feeble organic acids, immediately parts with its carbonic acid, and 

 gives a sodium salt of the acid taken. Furthermore, its solutions 

 already exhibit an alkaline reaction on litmus, and in many cases are 

 able to act as an alkali. Thus, for instance, sodium carbonate, like the 

 alkalis, aids the passage of certain organic substances (tar, acids) into 

 solution, and is therefore used, like alkalis and soap (which also acts 

 by virtue of the alkali it contains), for the removal of certain organic 

 substances, especially in bleaching tissues in cotton and similar works. 

 Besides which, a considerable quantity of sodium carbonate is used 

 for the preparation of sodium hydroxide or caustic soda, which has 

 also a very wide application. In large chemical works where sodium 

 carbonate is manufactured it is usual to first manufacture sulphuric 

 acid, and then by its aid to convert common salt into sodium sulphate, 



