SODA PROCESS. 4/3 



by the second the sulphuret of sodium is converted into carbo- 

 nate of soda ; and, if desirable, these changes may be effected 

 separately, by calcining the sulphate with coal and carbonate of 

 lime in succession. The lime becomes at the same time sul- 

 phuret of calcium, a compound which would destroy the carbo- 

 nate of soda, if dissolved along with that salt, in the subsequent 

 lixiviation of the ball soda. But although possessed of a 

 certain degree of solubility, the sulphuret of calcium does not 

 dissolve in the experiment, from being in combination with 

 lime, as an oxisulphuret of calcium. Hence an excess of lime 

 is necessary in the process. The application, however, of very 

 hot water to the ball soda is to be avoided, as the oxisulphuret 

 is decomposed at a high temperature, and sulphuret of calcium 

 dissolved out. The following diagram will represent the chemi- 

 cal changes in this process, supposing for simplicity that char- 

 coal is employed instead of coal, and lime instead of its carbon- 

 ate ; the numbers denoting equivalents : 



REACTION IN THE SODA PROCESS. 



Before decomposition. After decomposition. 



4 Carbon 4 Carbon - _ 4 Carbonic oxide. 



Snlnhate f 4 Ox yg en ^ 

 ouipnatc J o i o j 



f * j < ooaium - ooaa. 



of soda. I Sulfur ^^ 



T . / Oxygen " 



\ Calcium- ^ Sulphuret of calcium >3 



Lime Lime - Lirne 



The soda derives carbonic acid from the carbonate of lime or 

 from the fire, and is therefore obtained principally as carbonate. 

 The insoluble oxisulphuret of calcium of this process is known 

 as soda-waste. It has hitherto been not merely valueless but 

 troublesome to the manufacturer. But the attempt is at pre- 

 sent made to turn it to account as a source of sulphur. Means 

 are taken to condense the hydrochloric acid, formerly sent up the 

 chimney, and this acid is applied to the soda-waste, from which 

 it disengages sulphuretted hydrogen, and carbonic acid. But 

 hydrochloric acid is not produced, in the soda process, in ade- 

 quate quantity for this application of it, and carbonic acid 

 evolved with sulphuretted hydrogen might interfere with the 

 combustion of the latter. These difficulties, however, are in a 

 great degree removed by the discovery of Mr. Gossage, that 



