330 NITRATE OF POTASH. 



896. A mixture or compost of lime and salt is a 

 good manure; it contains carbonate of soda and chlo- 

 ride of calcium, both of which are useful to plants. 

 It is possible that salt when applied to land is always 

 more or less decomposed in this manner, and that, 

 according to the extent in which this takes place, 

 salt produces a beneficial effect. 



897. Common salt is a necessary addition to the 

 soil in the cultivation of marine plants, or such as 

 naturally grow near the sea-shore. It is also fre- 

 quently used to kill insects. For all these purposes 

 the most impure salt may be used; the impurities for 

 the most part rather increase the value of the sub- 

 stance as manure (252). 



898. Nitrate of potash has long been used as a 

 manure, being found to produce beneficial effects on 

 most soils, in quantities from one to three hundred 

 weight per acre. The exact nature of the chemical 

 effect produced by alkaline nitrates on plants is not 

 accurately known ; but as both nitric acid and fixed 

 alkali are separately valuable as manure, or at least 

 are found to assist vegetation, we might reasonably 

 expect that the nitrates should be good manures ; it 

 must always be remembered, however, that though 

 they contain both nitrogen and alkali, they cannot 

 well be used alone on ordinary soils, and are best 

 employed in conjunction with some other substance 

 containing phosphoric acid. 



899. A great many rich and fertile soils are found 



