60 AGRICULTURE FOR COMMON SCHOOLS 



will depend upon the amount in the rock used. Acid phos- 

 phate is very extensively used. 



The potash fertilizers are also from organic and chemical 

 sources. 1. The chief organic source is ashes, wood ashes 

 being the common source. The amount of potash in wood 

 ashes differs with the kind of wood from which the ashes are 

 obtained, as, for example, the unleached ashes from oak 

 contain about 10 per cent, of potash, from beech 16 per cent., 

 from elm 24 per cent. Hard wood contains more potash than 

 soft wood. Ashes also contain large quantities of lime and 

 small quantities of phosphoric acid, magnesia, and soda. 

 Unleached ashes are the only kind that should be used as a 

 fertilizer. By leached ashes we mean ashes that have been so 

 soaked by water that the potash has dissolved and run away. 

 2. Tobacco stems contain from 6 to 10 per cent, potash, and 

 are much used for mixed fertilizers. 



The chief chemical source of potash is the German pot- 

 ash mines in Germany. At Stassfurt in Germany there 

 are large deposits of salts which are rich in potash. 1. Kainit 

 is the name of one of these salts which is sold on the market 

 without having been treated in any way except grinding. It 

 contains about 12 to 13 per cent, of potash. It has consid- 

 erable magnesia and common salt mixed with it. Kainit is 

 rather quickly available when applied to the land. 2. Muri- 

 ate of potash is the name given to a potash fertilizer made 

 from certain kinds of the German salts by a process called 

 recrystallization. It contains about 50 per cent, of actual 

 potash and is considered the cheapest source of potash for 

 fertilizing. It is very extensively used. 3. Sulphate of pot- 

 ash is another potash fertilizer made from the German salts, 

 by the process of recrystallization in which those crystals con- 



