48 AMERICAN MANURES. 



which contain a considerable amount of this 

 substance. It also enters largely into the com- 

 position of the leaves of some trees, as the beech 

 and red pine. The presence of decaying veget- 

 able matter will also separate silica from its 

 insoluble compounds, as before stated. This is 

 one of the great benefits derived from green 

 manuring. The lack of soluble silica vitally 

 affects the growth of nearly all cultivated plants ; 

 but, as it can be economically manufactured and 

 applied to the soil as silicate of soda, and also 

 added in the waste products of previous crops, 

 the farmer has full supplies at command. 



CARBON. 



Carbon was discovered by Lavoisier in 17SO. 

 It enters largely into the composition of plants. 

 It forms the bulk of mineral coal, charcoal, lamp- 

 black, black-lead, and is exhibited in its purest 

 known state in the diamond. All these sub- 

 stances have the common property of uniting 

 with oxygen in a state of combustion, and then 

 producing carbonic acid gas. 



Carbonic Acid is composed of one equivalent 

 of carbon combined with two equivalents of 

 oxygen. Its salts are termed carbonates. That 

 plants assimilate this gas, and that it is the 

 most important source of carbon necessary to 



