IX.] SALT 269 



stiffening effect is similarly explicable by the extra 

 potash made available for the barley plant. Even the 

 ill effects of salt upon the malting quality of the barley 

 that are sometimes experienced, can be paralleled by 

 the observed effects of potash in prolonging the growth 

 of barley and deepening the colour of the grain. Salt 

 is also credited at times with injuring the tilth of heavy 

 soils and rendering them sticky and wet ; this effect 

 again is paralleled by the action of potash salts (p. 176) ; 

 an interaction takes place between the salt and the 

 carbonate of lime in the soil, and a little free alkaline 

 carbonate is formed, which deflocculates the clay. 



We may therefore conclude that the action of salt 

 is entirely indirect, rendering available the potash in the 

 soil instead of itself feeding the crop. None the less it 

 forms a valuable adjunct to other manures for all crops 

 requiring large supplies of potash, such as mangolds and 

 other root crops, and may greatly economise if not 

 entirely replace the use of potash salts themselves. In 

 some districts a waste product termed "gunpowder 

 salt " is obtainable ; this is the bye-product in the 

 manufacture of saltpetre by the interaction of nitrate of 

 soda and potassium chloride, and is identical with 

 common salt except that it also contains a little nitrate 

 and some potash. These technical impurities render it 

 more valuable for agricultural purposes, so that it forms 

 a very excellent top dressing for mangolds. 



Sulphate of Magnesia. — The action of this salt has 

 already been explained (p. 262) ; it is never required to 

 supply the plant with magnesia, sufficient quantities of 

 which are to be found in all ordinary soils for the needs 

 of the crop, and while it would render available some 

 potash in the soil, common salt will do the same thing 

 more cheaply. Carbonate of magnesia has from time 

 to time been suggested, and even put upon the market, 



