218 



SOILS AND FERTILIZERS 



applied safely to crops, as tobacco and potatoes, which 

 would be injured in quality if muriate of potash were 

 used, or if much chlorine were present. Low-grade 

 sulphate of potash is 90 per cent pure. 



252. Miscellaneous Potash Salts. Carnallit, 9 per 

 cent K 2 O, composed of KCl,MgCl 2 ,6 H 2 O. Polyha- 

 lit, 15 per cent K 2 O, composed of K 3 SO 4 ,MgSO 4 . 

 (CaSO 4 ) 2 ,H 2 O. Krugit, 10 per cent K 2 O, -- composed 

 of K 2 SO 4 ,MgSO 4 ,(CaSO 4 ) 4 ,H 2 O. Sylvinit, 1 6 to 20 per 

 cent K 2 O, composed of KCl,NaCl and impurities. 

 Kieserit, 7 per cent K 2 O, composed of MgSO 4 and 

 carnallit. 



253. Wood Ashes. For ordinary agricultural pur- 

 poses, wood ashes are an important source of potash, 

 although they are exceedingly variable in composition. 

 When leached the soluble salts are extracted and there 

 is left only about I per cent of potash. In unleached 

 ashes the amount of potash ranges from 2 to 10 per 

 cent. Soft wood ashes contain much less potash than 

 hard wood ashes. Goessmann gives the following as 

 the average of 97 samples of ashes : ^ 



