POTASSIUM FERTILIZERS 167 



p. 94. The liquor that is used for dissolving the carnallite 

 comes from various sources, and consists of washings from 

 the final potassium chloride and other mother liquors. This 

 liquor is run into the dissolver, and steam is injected till the 

 liquid begins to boil, and then the crude carnallite is intro- 

 duced. The specific gravity is kept at about 1*3, so as to 

 obtain a maximum separation of potassium chloride. The 

 operation of dissolving only takes about half an hour. 



The solution now has to be clarified by allowing it to rest 

 for an hour or two in special vessels. This clarification may 

 be assisted by sprinkling on the surface a little milk of lime. 

 As in the case of the manufacture of nitrate of soda, if large 

 lumps are employed it is necessary to have a second boiling. 

 The ordinary liquids passing away for crystallization contain 

 about 10 % of potassium chloride, 5 % of sodium chloride 

 and 20 % of magnesium chloride, with only a small quantity 

 of other salts. The waste carnallite contains about 3 % of 

 potassium chloride, 50 % of sodium chloride and 30 % of 

 magnesium chloride. This residue has been used to fill up 

 the old workings in the mines. 



The crystallizing vessels, into which the liquors are run, 

 are wrought-iron tanks of about 300 cub. ft. capacity, with 

 bottoms slanting a little to one side, where there is a plug 

 for running off the mother liquor. Arrangements are gener- 

 ally made for shutters to keep air away from the vessels and 

 to prevent too rapid cooling ; when rapid cooling takes 

 place the crystals are small and slimy. The salt first precipi- 

 tated carries down some materials in suspension, and is 

 usually not so pure as subsequent salts. The bottom salts 

 contain about 55 % of potassium chloride and 30% of sodium 

 chloride ; the side salts contain about 60 % of potassium 

 chloride and 25 % of sodium chloride. The mother liquor 

 that is drawn away from the crystallizing tanks still contains 

 about 20 % of the total potassium chloride, but a portion is 

 used to dissolve fresh crude salts and the remainder is concen- 

 trated by evaporation, until on cooling nearly the whole of 

 the potassium chloride present is recovered as artificial 

 carnallite. The concentration in a modern plant is usually 



