156 POTASH MANUKES 



the case with mangolds. Potash manures are best applied in the 

 autumn or winter so as to be well diffused through the soil before the 

 plant requires them. Little loss through drainage need be feared. 



Muriate of Potash is usually sold as guaranteed to contain 80 

 per cent KC1 (equivalent to about 51 per cent K 2 0). 



The Double Sulphate of Magnesium and Potassium actually 

 occurs crystallised with six molecules of water as Schonite 

 MgS0 4 .K 2 SO 4 .6H 2 0, and then contains, theoretically, about 44 per 

 cent of K 2 SO 4 : practically, 42 per cent is about the average. The 

 commercial product is calcined, whereby a portion of the water is 

 expelled, and the residue then contains on the average 48 per cent 

 K 2 S0 4 (equivalent to 26 per cent K 2 0). It usually contains about 2 

 per cent of lime and 2^ per cent of chlorine. 



Sylvinite contains varying quantities of common salt, water, etc., 

 and is not often used as a manure in England, though it is imported 

 into America. Its average content of potassium is said to correspond 

 to 16 or 17 per cent K 2 0. 



Sulphate of Potash is usually of from 90 to 95 per cent purity 

 (49 to 51 per cent K 2 0), and is too high priced to be often employed 

 in agriculture. 



Kainite is the most widely used potash manure. This substance, 

 the exact constitution of which has not yet been determined, is the 

 mineral itself, crushed or ground. Its composition varies, doubtless 

 owing to its admixture with other minerals, especially carnallite and 

 rock-salt, occurring in association with it. 



The proportion of potash varies from 12 to 20 per cent, being 

 usually near the lower figure. The sodium chloride varies from 25 to 

 45 per cent. It also contains lime, magnesia and sulphates. The 

 presence of much magnesium chloride is objectionable, since this 

 compound is deliquescent. 



The table on the following page gives the average composition of 

 the various commercial preparations. 1 



IY. MISCELLANEOUS MANURES. Under this heading may 

 be classed substances which contain none of the three chief manurial 

 ingredients, potash, phosphoric acid and nitrogen, but convey to the 

 soil some other constituent of plant food, or effect by their action upon 

 the soil the liberation of some necessary plant food from the insoluble and 

 unavailable condition. Among the most important are the following : 



Common salt. 



Gypsum. 



Lime and chalk. 



Ferrous sulphate. 



Gas lime. 



1 Lierke, Agricultural Chemist to the Verkaufs-Syndicat der Kaliwerke, Leo- 

 poldshall-Stassfurt. 



