FERTILIZERS AND MANURES. 



69 



The essential elements of plant food — viz., potash, 

 nitrogen and phosphoric acid — may now be purchased in 

 the markets combined in proportions to suit all demands, 

 as complete or partial manures. A short discussion of 

 their origin and properties is not out of place in a book 

 of this character. 



1.— POTASH. 



The German deposits of crude potash salts furnish the 

 largest supply of this important fertilizer to the markets 

 of the world. The chief forms in which these salts occur 

 in the mines are sulphate and nitrate (chloride) and 

 kainit, which is a combination of chlorides of magnesium 

 and sodium, magnesium sulphate and potassium sul- 

 phate. The kainit is largely used in the manufacture of 

 commercial fertilizers containing potash. The ashes from 

 cotton-seed hulls is a valuable source of potash, and a 

 good market for this southern product has been created 

 within the past few years since the sale of cotton-seed oil 

 has become such an important item. The hulls, after 

 extracting the interior of the seeds, are used for fuel in 

 the manufacture of oil, and the resulting ashes are 

 sacked and sold for fertilizers. When the hull ashes are 

 mixed with "nitrogenous organic materials great caution 

 is to be observed, since mixtures of this kind, if kept for 

 any length of time, especially if allowed to become moist, 



