Mr. J. Bi-own on the Products of the Soda Manufacture, 19 



this manner all the gas is absorbed. At the expiration of 

 about two hours the evolution of gas ceases; and the sulphate, 

 which is in a semifluid state, is removed to another chamber, 

 where it is strongly heated in order to drive off the whole of 

 the acid. The whole operation takes about four hours. 



The foreign matters contained in the sulphate of soda thus 

 obtained are sand, peroxide of iron, magnesia and undecom- 

 posed salt. 



To estimate the sand. This remained as insoluble matter 

 when the sulphate was digested in water containing muriatic 

 acid, and was separated by filtration. 



1000 grains of sulphate of soda gave 2-82 grains of sand. 



3-38 

 Average 3*10 



From the solution filtered from the sand the peroxide of 

 iron was precipitated by ammonia, muriate of ammonia having 

 been previously added to retain the magnesia in solution. 



1000 grs. of sulphate of soda gave 2-15 grs. peroxide of iron. 



Average 2-30 

 After separating the sand and peroxide of iron, as men- 

 tioned above, the lime was precipitated by oxalic acid and 

 caustic ammonia. 



CaO.COj. CaO.SOg, 

 1000 grains of sulphate of soda gave 7'000 9"656 



7-367 10-019 

 ... * ... 7-100 9-520 



Average 9*731 



The solution thus freed from lime, &c. was treated with 

 ammonia and phosphate of soda. The magnesia was thus 

 separated as ammonio-phosphate. 



2MgO, P2 0,. MgO.SO 

 1000 grains of sulphate of soda gave 2*70 2-893 



The quantity of chloride of sodium was ascertained by pre- 

 cipitating the chlorine by nitrate of silver and nitric acid. 



Ag CI. Na CI per 1000 grs. 

 200 grains of sulphate of soda gave 4-30 8-995 



1000 ... ... 29-70 12-373 



500 ... ... 13-80 11-500 



Average 10-956 



The sulphate of soda always contains a small quantity of 

 free acid, the amount of which was ascertained by determining 

 the weight lost by heating to redness. 



C 2 



