42 THE CHEMISTEY OF THE FARM. 



those most benefited by burnt lime. In reclaiming peat 

 bogs lime is of the highest value. The acid humic matter 

 of the peat is neutralised by the lime, and the conditions 

 thus made suitable for the oxidation of the nitrogenous 

 organic matter and the production of ammonia and 

 nitrates. 



The general effect of lime is to render available the 

 plant food already in the soil, without itself supplying 

 any significant amount ; liming cannot, therefore, be 

 successfully repeated except at considerable intervals. 



Potassium Salts. These salts are now obtained from 

 Stassf urt and Leopoldshall in large quantities ; they form 

 a thick deposit overlying an enormous mass of rock salt. 

 The commonest potassium salt employed as manure, is 

 'kainite ; it consists of chloride of potassium, sulphate of 

 magnesium, and water, with the chlorides of sodium and 

 magnesium in addition. Kainite will contain about 13 

 per cent, of potash. 



Wood ashes may also be employed as a potash 

 manure ; they will contain between 5 and 10 per cent, of 

 potash. The ash of young boughs is richer than that 

 from full -si zed timber. 



Potash manures produce their greatest effect on pas- 

 ture ; clover, potatos, and root crops may also be bene- 

 fited by their use. Many soils, especially clay soils, are 

 naturally well furnished with potash; on these soils 

 potash manures are almost without effect. 



Common Salt. Chloride of sodium supplies no essen- 

 tial ingredient of plant food. Salt is commonly used for 

 mixing with nitrate of sodium, and as a manure for 



