ACTION OF SALTS OF AMMONIA ON PHOSPHATES. 79 



root-plants, which serve more particularly as food for 

 cattle, Avith a greater power of taking up chloride of 

 socUum from the soil than is possessed by other plants ; 

 and agricultural experience shows that the presence 

 of a small amount of common salt is favourable to the 

 luxuriant groAvth of these plants. 



Of nitric acid, it is generally assumed that it may, like 

 ammonia, serve to sustain the body of the plant. Thus, 

 chloride of sodium and the nitrates act in two distinct 

 ways : one direct, by serving as food for the plant ; one 

 indu'ect, by rendering the phosphates available for the 

 purposes of nutrition. 



The salts of ammonia act upon earthy phosphates in 

 the same way as the salts just mentioned, but with this 

 distinction, that then- power of dissolvmg phosphates 

 is far greater ; a solution of sulphate of ammonia ^vill 

 dissolve twice as much bone-earth as a solution of an 

 equal quantity of chloride of sodium. 



However, as regards the phosphates in the soil, the 

 action of the salts of ammonia can hardly be more 

 powerful than that of chloride of sodium or nitrate of 

 soda, since the salts of ammonia are decomposed by the 

 soil much more speedily, and often even immediately ; so 

 that, as a general rule, no solution of such a salt can be 

 said to be actually moving about in the soil. But as a 

 certain volume of earth, however small, is required to 

 decompose a given quantity of salts of ammonia, the 

 action of those salts upon this small volume of earth 

 must be all the more powerful. While, then, the action 

 of salts of ammonia is barely perceptible in the somewhat 

 deeper layers of the arable surface soil, that which they 

 exercise on the uppermost layers is so much the stronger. 

 Feichtinger observed that solutions of salts of ammonia 

 decompose many silicates, even felspar, and take up 



