POTASSIC MANURES 109 



time as the double salt of potassium and mag- 

 nesium, which is hardly soluble. This mixture 

 of residual salts often contains 7.5 per cent of 

 potassium, which corresponds to 12 per cent 

 of potassium chloride, or 14 per cent of potas- 

 sium sulphate. It is utilized by either extracting 

 the common salt from it or by converting it into 

 manure of low strength. In rational manufac- 

 ture the residual salt should be washed in the 

 pan itself; for this purpose the mother liquor 

 No. 2 is used, as the salt as well as the pan itself 

 is still very hot. When the evaporated solution 

 is run off, the mother liquor with which the 

 pan is drenched heats rapidly and dissolves the 

 greater part of the potassium salt which is still 

 contained therein. This solution is facilitated 

 by stirring. When the density of the solution 

 determined while boiling reaches 34 to 35 Be., 

 it is run through wrought-iron gutters into 

 special crystallizers, where it deposits not po- 

 tassium chloride, but a salt with tetrahedral 

 crystals, the composition of which is analogous 

 to carnallite. If the solution was sufficiently 

 concentrated, the liquid which flows from the 

 carnallite crystals (the final liquid) only contains 

 1 to 2 per cent of potassium chloride. In certain 

 factories the bromine is extracted, in others 

 the magnesia. The artificial carnallite thus 

 obtained is dissolved in water in smaller pans 

 than those used to dissolve the crude salt. The 

 solution tested to 32 to 33 Be. is run into vats, 



