140 CHEMISTRY OF FARM PRACTICE 



chloride and calcium sulphate. Sylvinit consists mainly of 

 potassium chloride and sodium chloride. Overlying the 

 potash region is a layer of impervious clay, which has 

 served to keep out water and prevent the loss of these 

 salts by leaching. Above this clay are the following strata : 

 anhydrite, gypsum, clay, sand, and limestone. 



The value of these salts was discovered about 1860, 

 the potash salts having formerly been bored through and 

 discarded as worthless, while the rock salt below was mined. 

 Since the discovery of the value of these salts, the mining 

 of them has been regulated by the German Government, 

 which derives a large income from the export tax which is 

 imposed. 



100. Wood Ashes. Before the discovery of the Stassfurt 

 potash deposits, the main source of potash was wood 

 ashes. The potash content of these ashes is in the car- 

 bonate and sulphate forms. Ashes also contain a con- 

 siderable percentage of lime, and a small percentage of 

 phosphorus. Ashes from hardwood trees are higher in 

 their potash content than other ashes. In conserving 

 ashes for their potash content, they should be stored in 

 a covered pit with impervious sides and floor, for the potash 

 is readily leached out. 



101. Organic Sources of Potash. Some organic materials 

 contain appreciable amounts of potash. Tobacco stalks 

 and stems contain from 4 to 8 per cent of potash. Cotton- 

 seed and flaxseed each contain some potash. Cottonseed 

 contains about 1| per cent of potash, cottonseed meal about 

 1| per cent, cottonseed hulls about 1 per cent, and cotton- 

 seed hull ashes about 24 per cent. Linseed meal contains 

 about If per cent potash. 



The pomace obtained from the fermenting of wine 

 contains some potash and some nitrogen. 



102. Minor Sources. Another source of potash is kelp, 

 the ashes of seaweeds. Kelp contains from 4 to 20 per 

 cent of potash, depending upon the seaweed burned. 



