236 POTASH FERTILIZERS 



extent. Loss of calcium from soils is hence not so great as 

 in the case of the chloride. 



180. Kainite. — This fertilizer was formerly the mineral 

 of the same name, the formula of which is KCl.MgSO4.6H2O, 

 but at present it is merely a name for a potash fertilizer 

 containing 12 per cent, potash, the form of the potassium 

 and the other compounds varying considerably. The per- 

 centage of potash only is constant. Since kainite always 

 contains chlorine in some form, it is open to the same 

 objection as is the muriate of potash, but it is nevertheless 

 a good low grade form of potash. 



181. Wood Ashes. — One of the oldest sources of potash is 

 wood ashes. When clean, hard wood is carefully burned, the 

 potash content may run up to 8 or 10 per cent., mostly in the 

 carbonate form. In addition there may be 1 or 2 per cent, of 

 phosphoric acid, and 30 per cent, of calcium compounds, 

 the calcium being in the oxide form when fresh burned, 

 but changing to carbonate on exposure. The wood ashes 

 now on the market are of a very inferior grade, carrying 

 not more than 3 or 4 per cent, of potash in unleached ashes. 

 Leached ashes, that is, ashes which have been leached to 

 extract potash for other purposes than for fertilizers, or 

 ashes which have been exposed to the weather and leached 

 by rain, contain usually less than 1 per cent, potash. 



Potassium carbonate in wood ashes is a good fertilizer 

 unless too much is applied, when it has a deflocculating 

 effect on soil grains and is poisonous to plants. This car- 

 bonate and the calcium carbonate in wood ashes are both 

 neutralizes of soil acidity and are valuable for this purpose. 



182. Kelp and Alunite. — The only sources of potash in 

 the L^nited States of any consequence are the giant kelps 

 or seaweeds on the Pacific coast (Fig. 55), and alunite, a 

 mineral found to some extent in Utah, and consisting of a 

 double sulphate of potassium and aluminium. The giant 

 kelps grow rapidly and sometimes attain a length of hundreds 

 of feet. Dry, they contain 15 to 20 per cent, potash and their 

 ashes contain as much as 30 to 35 per cent, potash in the 

 form of the chloride. Alunite contains 10 per cent, potash, 

 but can be ignited and the potash content increased to 15 



