POTASSIC MANUEES. 307 



Potassium Suljjhate. — This salt is manufactured at Stassfurt, 

 by drenching potassium chloride with sulphuric acid and calcining 

 in a reverberatory furnace. The reaction which takes place is the 

 same as that used to manufacture sodium sulphate from common 

 salt and sulphuric acid. First of all the material heats, gaseous 

 hydrochloric acid is given off, and acid potassium sulphate formed 

 according to the equation — 



KCl + H,SO, = HKSO, + HCl. 



Afterwards, the temperature continuing to rise, the acid sulphate of 

 potassium being weak acts on the remainder of the potassium chloride. 

 A new disengagement of hydrochloric acid gas is produced, and 

 finally potassium sulphate as a solid mass. This reaction is ex- 

 pressed by the equation — 



KCl + HKSO^ = K,SO^ + HCl. 



As the potassium sulphate as it comes from the furnace is in big 

 lumps, it must be crushed before delivery to farmers. In the same 

 way as the price of potassium chloride is calculated on the basis of 

 an 80 per cent salt, that of potassium sulphate is based on a 90 per 

 cent salt, consequently 100 lb. of this product at 95 per cent equal 

 110 lb. at 90 per cent. Potassium sulphate of 96 per cent strength 

 is worth about 2^d. more a cwt. on the 90 per cent basis than the 

 product which only tests 90 per cent. 



Double Suljjhate of Potassium and Magnesium. — This product 

 has already been mentioned as schoenite, but is never found in that 

 form ; it is manufactured in large quantities from kainit. It consists 

 of equivalent quantities of potassium sulphate and of magnesium 

 sulphate, and contains in the crystalline state six equivalents of water. 

 The method of manufacture varies with the factories, but all pro- 

 cesses are based on the lixiviation of the magnesium chloride and 

 common salt from the kainit by hot saline solutions. The dried 

 ground salt contains about 48 per cent of potassium sulphate corre- 

 sponding to about 26 per cent of potassium, and it is put on the 

 market w^ith the guarantee of a maximum content of 2*5 per cent of 

 chlorine. This salt is much used as a manure. 



It possesses the following composition, according to Mercker : — 



TABLE CIV.— ANALYSIS OF SCHOENITE. (MEECKER.) 



Per cent. 

 Potassium sulphate . . . . . • .50-4 



Magnesium „ ....... 34-0 



Common salt . . . . • • • . 2-o 



Water 11-6 



Its potassium content is therefore 27"2. 



Double Carbonate of Potassium and Magnesium. — The salt 

 contains 17 to 18 per cent of potassium; it consists chiefly, as its 

 name indicates, of the carbonates of potassium and magnesium with 



