Objects to be Accomplished by Plowing. 143 



Carbonic acid is one of the most active of the agents employed 

 in bringing the insoluble inorganic matter in the soil into that 

 physical condition when they become available as plant food; in 

 order that this acid may be formed, it is essential that the car- 

 bonaceous matters in the soil should be brought into direct contact 

 ■with the atmosphere from which they procure the oxygen neces- 

 sary to convert them into carbonic acid. 



So long as staofnant water remains in the soil, or so lono; as it 

 is in a dense and very compact condition, it is impossible for the 

 carbon in the soil to be converted into acid. 



A supply of available phosphatic salts is essential for the 

 growth of most cereal plants, but these salts often exist in great 

 profusion in the soil without contributing in any way to the nutri- 

 tion of plants, because they are in an insoluble condition. If 

 now water charged with carbonic acid is allowed to circulate 

 through the hard phosphatic nodules a portion of them will be 

 dissolved by the acid and diflused by the water among the pores 

 of the soil where they will be fixed in readiness for the demands 

 of the growing plants. In this case we see another way that the 

 fertility of the soil is increased by pulverization, because the air 

 is admitted to the soil, which becomes the agent of converting 

 the carbon existing in it into carbonic acid, which in its turn ren- 

 ders many substances which were previously useless very efficient 

 in promoting the growth of plants. 



Mr. Way shows that the agents which exercise the greatest 

 power in retaining manurial substances in physical combination 

 with the soil are the double silicates, which we will endeavor to 

 explain briefly, as their recent investigation has probably pi-e- 

 vented a large proportion of the users of the plow from becoming 

 fully acquainted with their properties. 



If pure sand or powdered quartz be fused with lime, alumina 

 or some other alkali, they become chemically united, and are 

 known as silicates. Thus, silica combined with potash is called 

 silicate of potash; with ammonia, silicate of alumina, etc. These 

 substances, under favorable circumstances, are very prone to unite 

 together. Thus, silicate of alumina and silicate of lime are often 

 found united together as one well marked substance havino; 

 definite characters. These new compounds are called double 

 silicates. They have the power, in a remarkable degree, of 

 exchanging bases in a certain prescribed order. Thus, when the 

 double silicate of aluniinu and soda is digested with a solution of 



