POTASSIC MANURES. 



303 



sludge with it, different arrangements have been made to retain it. 

 After the clarified solution has been run off, it is led through a 

 wrought-iron gutter into underground crystallizers. As the solution 

 cools in flowing through the gutters, it deposits a certain amount of 

 salt containing 45 to 50 per cent of potassium chloride. This gutter 

 salt is most generally used in manure manufacture. It is generally 

 treated with potassium chloride of a higher strength. 



Crystallization.— The crystallizers in w^hich the solution cools 

 and forms crystals of potassium chloride are of riveted wrought- 

 iron like the clarification basins ; they vary in size and shape, some- 

 times flat because the solution cools more quickly therein, some- 

 times deep because they occupy less space and yield larger crystals. 

 When the solution is cold, which takes two to four days, the mother 

 liquor II is decanted from the crystals of potassium chloride ; it is 

 run off by the gutters fixed under the crystallizers into wrought-iron 

 basins or into masonry ones lined with cement. It is used either to 

 dissolve the crude salt or treated directly as will be described further 

 on. The potassium salt which is deposited in the crystallizers 

 consists of a mixture of potassium chloride and common salt ; it is 

 stifl soiled by adhering mother liquor. It crystallizes in the same 

 form as sylvine, with this difference that the crystals are not always 

 perfect ; their size depends chiefly on the density of the solution of 

 crude salt. When that has a density of 32° to 33° B., or a still weaker 

 density, crystals often one centimetre wide, of a pearly lustre^ are 

 obtained. ' When the solution is more dense, say about 33° to 35° B., 

 it forms soft crystalline needles. It is clear that the size of these 

 crystals must ^considerably affect the purity of the potassium 

 chloride, as attenuated crystals must retain more mother liquor 

 than large ones, and that consequently they contain more magnesium 

 chloride. The impure, fine, granular salt often only contains but 60 

 per cent of potassium chloride, whilst the salt with large crystals 

 yields on analysis : — 



TABLE CI.- 



Insoluble 



-ANALYSIS OF CRYSTALS FEOM POTASH SALT 

 CRYSTALLIZERS. 



Per cent. 

 0-0876 



Magnesium sulphate 

 „ chloride 

 Potassium „ 

 Common salt 



1-2468 



6-9072 



68-1504 



23-5560 



99-9480 



It may be remarked in passing that the salt that is deposited on 

 the sides of the crystallizers is always more pure than that de- 

 posited at the bottom. To obtain high strength products, a portion of 

 the two sorts may be taken, especially for continuing the treatment. 



