32 Preparation of Substances 



In all this work it is the object to precipi- 

 tate a salt by mixing two hot saturated solu- 

 tions. The appearance of ciystais or a scum 

 (film of fine crystals) on the surface may be 

 taken as an indication of saturation. Mixing 

 solutions which are not saturated may result 

 in large loss of the desired substance. Often 

 the addition or withdrawal of one cubic 

 centimeter of water is all that is necessary 

 to produce the condition sought. 



In dissolving the double sulfate in water the 

 salt may not appear to dissolv completely. 

 This is immaterial as the residue is potassium 

 sulfate, the same as the desired product. It 

 is possible to crystallize out potassium sul- 

 fate by evaporating the solution of potash- 

 magnesia sulfate. 



Muriate of pota^sh is sold in three grades 

 containing 80, 95 and 98 per cent, respec- 

 tively. The material containing 80 per cent 

 potassium chlorid is the grade mostly used 

 for fertilizers. This is produced industrially 

 by treating the raw salts as they are mined 

 with a hot saturated solution of magnesium 

 chlorid such as is thrown away at the end 

 of this experiment. The resulting hot solu- 

 tion is coold in cement tanks and the crude 

 muriate of potash separates out. The crys- 

 tals are centrifuged and further dried over a 

 fire in sloping pans about 10 x 60 feet in 



