MANUFACTURING THE CONCENTRATED SALTS 493 



used in the manufacture of the cheaper grades of glass. From 

 the residuum of the first solution of carnallit, treated with cold 

 water, kieserit (sulfate of magnesia) settles out in fine crystalline 

 particles, and is moulded into blocks. Large quantities of bromin 

 and iron bromid are obtained at the end of the process. Some 

 of the Stassfurt factories also prepare calcined magnesia, hydrate 

 of magnesia, calcium chlorid, carbonate of potash, carbonate of 

 potash-magnesia, etc. 



In order to obtain the complete extraction of potash, the pro- 

 cesses of manufacture are complex, and solutions and salts re- 

 quire repeated handling. It naturally follows that the separa- 

 tion of commercially pure salts from solutions of other salts is 

 an expensive process, and that it is only by the most painstaking 

 care and full utilization of every possible by-product that potash 

 salts can be produced and sold at the present low prices. 



Sulfate of potash is manufactured in less quantities than muri- 

 ate, owing to the smaller demand for it in the market; but its 

 consumption is rapidly increasing. There are several processes 

 of manufacture. The one in general use is to concentrate a solu- 

 tion of kainit to a certain specific gravity, and then allow it to 

 cool slowly in large crystallizing vats. The resulting crystals are 

 washed and dried, and form the commercial salt sulfate of potash- 

 magnesia, containing generally 40 per cent, of sulfate of potash, 

 but when calcined, 48 per cent. In the manufacture of sulfate 

 of potash a solution of sulfate of potash-magnesia and a given 

 quantity of muriate of potash are boiled together, whereupon 

 the less soluble sulfate of potash separates and falls as a precipi- 

 tate, after which the solution is boiled down to a certain specific 

 gravity, and cooled slowly in crystallizing vats, where the residual 

 potash separates as crystals of sulfate of potash. As it is sold, 

 it varies from 90 to 96 per cent, pure, equivalent to 46 to 52 per 

 cent, actual potash. 



The following tables give the average analyses of the more 

 important Stassfurt potash salts. The figures show the pounds 

 of various substances in 100 pounds of the different salts. 



The numerous by-products obtained in refining the crude potash 

 salts are utilized in many ways and for various purposes. Some 



