The Composition and Use of Fertilizers. 237 



also contains chlorides of sodium and magnesium. It is little 

 used in this country. 



Sulphate of Potash is another product of the German mines. 

 Strictly pure sulphate of potash contains about 54 per cent, of 

 actual potash, but the product found in the market is of variable 

 composition and purity. The highest grade of commercial sul- 

 phate of potash is 90 to 9'5 per cent, pure and contains from 48 

 to 51 per cent, of actual potash. Low-grade sulphates contain 

 as little as 30 per cent, of actual potash, together with more or 

 less sulphate of magnesia and common salt. 



Sulphate of Potash and Magnesia is known also as double 

 manure salts or simply as double potash salts. This material 

 comes from the German mines, and contains 48 to 52 per cent, 

 of sulphate of potash, equivalent to 26 to 28 per cent, of actual 

 potash. It also contains 32 to 36 per cent, of sulphate of mag- 

 nesia. 



^Titrate of Potash, commonly called saltpeter or nitre, is a 

 most valuable fertilizing material for potash and nitrogen also. 

 The demand for its use in the manufacture of gunpowder makes 

 it too expensive to use commonly as a fertilizer. It is found in 

 the market as " crude " nitrate of potash, containing about 44 

 per cent, of actual potash, and also as " double refined " nitrate 

 of potash, containing about 46.5 per cent, of actual potash. 



Cotton Seed Hull Ashes were produced in the South at the 

 cotton seed oil factories, where the hulls, after being removed from 

 the cotton seed, were used as fuel. Such ashes contain from 15 

 to 25 per cent, of potash, in addition to from 7 to 10 per cent, 

 of phosphoric acid. They formed a very valuable fertilizer and 

 were much used South in the manufacture of commercial fer- 

 tilizers. This material is not commonly found now. 



Tobacco Stems contain from 6 to 7 per cent, of potash and 

 about two per cent, of nitrogen. They are ground fine and often 

 used in making commercial fertilizers. 



Wood Ashes contain more or less potash, which is present 

 chiefly in the form of carbonate. The amount of potash in com- 

 mercial wood ashes varies from below 4 to 7 per cent., the 

 average being under five per cent. Wood ashes also contain be- 

 tween 1 and 2 per cent, of phosphoric acid. The amount of 

 potash in wood ashes depends upon a variety of conditions, such 

 as the kind and age of wood, the method of burning, and espe- 

 cially the way in which the ashes are stored. Where ashes have 



