POTASSIC MANURES. 



301 



It responds therefore to the formula — 



K,SO, + MgSO, + 2CaS0^ + 2Hp. 

 When treated with ^Yater it is the potassium salt which preferably 

 dissolves, whilst the magnesium sulphate and the calcmm sulphate 

 remain in great part undissolved. Before being discovered m the 

 Stassfurt mines polyhalite had been already met with m ditterent 

 places at Ischl, Hallein, Berchtesgaben, etc., partly as rhombio 

 crystals or fibres or minute crystalline rods. tit- 



6. Krugite has a chemical composition similar to polyhalite. 

 It responds to the formula — 



K^SO, + MgSO, + 4CaS0, + 2H,0. 



TABLE C.-ANALYSIS OF KEUGITE. (MEECKER.) 



Potassium sulphate 



Magnesium „ 



Calcium ,, 



Water 



Common salt . , 



Per cent. 



18-60 



14-70 



61-00 



4-20 



1-50 



100-00 



Density 2-801. , ^ , , - 



It now remains to describe the processes used to extract from 

 these minerals the whole series of products supplied to agriculture 



as potassic manures. . . j. , -ui mr,^ 



Manufacture of Potassium Chloride [muriate of PO^ash].— Ihe 

 crude salt treated consists of a mixture of all the salts described 

 above. However, carnallite predominates ; it forms 50 to 60 per cent 

 of the crude salt, equal to a potassium chloride content ot Id to U 

 per cent. The processes now used in the treatment of the crude 

 salt in the manufacture of more pure potash salts (potassium 

 chloride) are based essentially on the property of carnallite to de- 

 compose in presence of water into potassium chloride and magnesmna 

 chloride ; it is therefore dissolved and potassium chloride separated 

 from the solution by crystallization. The process is m itself very 

 simple ; what complicates it is the presence of quite a series ot 

 foreign salts accompanving the carnallite, the most important of 

 which are rock salt [NaCl], in the proportion of 20 to 25 percent 

 and kieserite [MgSO, + H.O], which forms lo to 20 per cent 

 of the crude salt. Other' minerals, such as kamit, polyhalite, 

 tachydrite CaCl.. + 2MgCl. + 12H,0, etc., are rarely met with m 

 large proportion,' but they t'hen are very troublesome in the process 

 CritJmig the Crude Salts.-As the mines deliver the crude salt 

 in big lumps (in the beginning they delivered them ground) they 

 must be crushed before being treated. Formerly they were satisfied 

 with crushing lumps by blows from a mallet with a long handle. 



