38 Chemical Changes in the Soil. [July, 



AGENTS WHICH PRODUCE CHEMICAL CHANGES IN 

 THE SOIL. 



It is well known at the present day that the soil is made up of 

 disintegrated rocks. This fact may be demonstrated by inspection 

 of the linest soil by the microscope. By this instrument v/e may 

 see that the soil is composed of quartz, feldspar, and in many in- 

 stances, mica, hornblende, and various other stones and rocks in 

 fine powder. Even the whole mass of soil may be seen to be thus 

 constituted. But soil, if it were wholly composed of particles suf- 

 ficiently coarse to be seen, would be almost barren; that is, it 

 would not be fitted to supply in that condition the necessary inor- 

 ganic matter. Hence it is necessary that it should be acted upon 

 still farther; that its particles in lact should be brought into a 

 soluble condition. The agents by which this is effected are water 

 and carbonic acid, together with a few other agents which assist 

 in the process. The substances to be dissolved seem to be among 

 the bodies the least soluble, as quartz or flint, mica, feldspar and 

 feldspar compounds, clay and clay slate, etc. It would farther 

 seem that by the slow operation of nature, that the soluble mate- 

 rials necessary for the growth of plants would hardly be formed 

 with sufficient rapidity to supply the wants of the vegetable 

 kingdom. 



Silex, sand or quartz, in its pure state, is insoluble either in 

 water or water charged with carbonic acid. When silica or sand 

 is boiled with soda, potash or lime, or ignited with either or all 

 of these alkalies together, the silica is dissolved and forms glass. 



Now silica exists in combination with these alkalies in the 

 rocks, stones, and in the soil, in a comminated state. In this state, 

 viz., in that which resembles artificial glass, and which is called 

 by chemists a silicate, the solution of the silex is far less difficult. 

 Even common window glass, or the common glass vessels, are 

 somewhat soluble in water, especially when the water contains 

 carbonic acid. Glass vessels in which water is distilled, although 

 heated only to 212° Fah. contain a portion of their substance dis- 

 solved, and this may be proved by evaporating the water, and it 

 may be found that the loss of weight sustained by the vessel is 

 equalled by the solid residue obtained by evaporation. 



So even window glass in certain situations after some conside- 

 rable exposure, becomes opake and rather resembles ground glass, 

 than the beautiful polished glass immediately from the manufac- 

 tory. The solubility of the silicates will be found to be in pro- 

 portion to the amount of alkalies present. 



Feldspar, which is vSO common in the primary rocks and even 



