POTASH MANUBES. 167 



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% KC1 (equivalent to about 51% K a O). 



The double sulphate of magnesium and potassium actually 

 occurs crystallised with six molecules of water as Schonit 

 MgS0 4 .K 2 S0 4 .6H 2 0, and then contains theoretically about 44% 

 of K 2 S0 4 : practically, 42 % is about the average. The commer- 

 cial product is calcined, whereby a portion of the water is ex- 

 pelled, and the residue then contains on the average 48% 

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

 lime and 2J% 01. 



Sylvinite contains varying quantities of common salt, water, 

 &c., 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% K 2 0. 



Sulphate of potash is usually of from 90 to 95% purity (49 to 

 51% K 2 0), and is too high priced to be often employed in 

 agriculture. 



Kainite is the most widely used potash manure. This sub- 

 stance, the exact constitution of which has not yet been deter- 

 mined, 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%, being 

 usually near the lower figure. The sodium chloride varies from 

 25 to 45%. It also contains lime, magnesia, and sulphates. 

 The presence of much magnesium chloride is objectionable, 

 since this compound is deliquescent. 



The following table gives the average composition of the 

 various commercial preparations" : 



* Lierke, Agricultural Chemist to the Verkaufs-Syndicat der Kaliwerke, 

 Leopoldshall-Stassfurt. 



