SOURCES AND COMPOSITION OF FERTILIZERS 



309 



Wood ashes are variable in composition, and their value 

 depends upon the kind of wood from which they are made, and 

 whether they are leached or unleached. Hard wood yields the 

 most valuable ash. Ashes exposed to the weather lose most of 

 their potash by leaching. Unleached ashes contain 4 to 8 per 

 cent, potash and about 2 per cent, phosphoric acid. 



Goessmann gives the following analyses of ashes : 



Coal ashes contain little plant food. Since ashes contain car- 

 bonate of lime and carbonate of potash, they are especially bene- 

 ficial to acid soils, or those needing lime. 



German Potash Salts. The German potash salts are mined and 

 concentrated in the region around Strassfurt, Germany, where 

 they occur in immense beds at depths of from 1500 to 2500 feet 

 below the surface. The important minerals found are as 

 follows : 



Carnallite, KC1, MgCl 2 , 6ELO. 



Kainit, K 2 SO 4 , MgSO 4 , MgCL,, 2H 2 O. 



Sylvinite, KC1, NaCl, K 2 SO 4 , MgCl 2 , 6H 2 O, MgSO 4 . 



Hartsalz, KC1, NaCl, MgSO 4 , H 2 O." 



Carnallite, the chief source of potash, usually occurs mixed with 

 rock salt and other minerals, and contains, as mined, about 9 per 

 cent, potash. Kainit, as mined, contains about 30 per cent, rock 

 salt and about 12 per cent, potash. Sylvinite is a mixture of 

 sodium and potassium chlorides, containing 14 to 18 per cent, 

 potash. The potash salts chiefly used in this country are kainit, 

 muriate of potash, and sulphate of potash. 



