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CHAPTER XC. 



POTASH MANURES, 



'\jTINERAL potash. Potash occurs in nature in felspars 

 and mica, which enter into the composition of every 

 soil. The pink coloured orthoclose felspar which is so com- 

 mon in Indian granites, is richest in potash. In felspars, 

 potash is contained in a more soluble form than in mica, and 

 its solubility is enhanced by admixture with lime. Zeolites 

 also contain potash and being more soluble than ordinary 

 felspar (with which they resemble in composition) are good 

 fertilisers, and they are abundantly present in some soils. 

 Potassium sulphate (K 2 S0 4 ), potassium chloride or sylvine 

 (KC1), potassium nitrate, and Kainit, also occur in nature. 



906. For ascertaining whether a substance contains 

 potash or not, the flame test may be employed. Potassium 

 gives violet flame ; the flame effect of sodium, of course, 

 must be eliminated by the use of dilute hydrochloride acid. 



-907. In Europe, potash manures are used chiefly in the 

 form of Kainit which is obtained from Prussia where it occurs 

 as a natural deposit at Stassfurt. Very few soils need 

 potash manures as mere plant-food, as usually there is 

 enough of available potash in every soil. The composition 

 of Kainit is represented by the formula K2SO 4 . MgSO 4 . 

 MgCl () . 6H 2 O. Common salt 'often occurs in Kainit as im- 

 purity. Ordinary Kainit contains 13 to 15 per cent, of K 2 O 

 and Calcined Kainit 17 to 18 per cent. Concentrated potash 

 salts are made out of this. Other sources of potash manure 

 are the mother liquor from sea water after the extraction of 

 common salt and vegetable ashes. 



908. Organic potash. The commonest potash manure is 

 ashes of all kinds. Liquors obtained by distillation of beet and 



