70 THE SOIL. 



arrested and retained at a point at which they can be 

 taken up by the roots of plants. 



2. Carbon in the soil causes it to appropriate 

 larger quantities of the fertilizing gases of the atmos- 

 phere, on account of its power, as just named, to ab- 

 sorb gases. 



The atmosphere contains gases, which have been 

 produced by the breathing of animals, by the decom- 

 position of various kinds of organic matter, which 

 are exposed to atmospheric influences, and by the 

 hiii-n ing of wood, coal, etc. These gases are chiefly 

 ammonia and carbonic acid, both of which are largely 

 absorbed by water, and consequently are contained 

 in rain, snow, and dew, which, as they enter the soil, 

 give up these gases to the carbon, and they there 

 remain until required by plants. Even the air itself, 

 in circulating through the soil, gives up' fertilizing 

 gases to the carbon, which it may contain. 



3. Carbon gives to the soil power to absorb 

 moisture, because it is itself one of the best absorb- 

 ents in nature ; and it has been proved by accurate 

 experiment that peaty soils absorb moisture with 

 greater rapidity, and part with it more slowly than 

 any others. 



4. Carbon in the soil renders it warmer, because 

 it darkens its color. Black surfaces absorb more heat 

 than light ones, and a black coat, when worn in the 

 sun, is warmer than one of a lighter color. By mix- 

 ing carbon with the soil, we darken its color, and 

 render it capable of absorbing a greater amount of 

 heat from the sun's rays. 



