1847.] Chemical Changes in the Soil. 39 



in sedimentary ones, may be regarded as a natural glass, or in 

 other words it is a silicate, and may be dissolved in water, though 

 slowly, especially if carbonic acid has access to it. Hence a soil 

 which is mixed with particles of feldspar, mica, or even clay slate, 

 and many other bodies containing fine particles of the silicates, 

 are actually dissolved in the common operations of nature which 

 are going on in the soil. These operations furnish potash or a 

 soluble silicate of potash, a substance required in all cereals and 

 grasses for the perfection and strength of the straw or stalk. An- 

 other property of silicate which the farmer ought to be familiar 

 with, is its insolubility after ignition or heating to redness, or 

 even partially so, by thorough drying. As this substance exists 

 in straw, and as straw is used as a fertilizer, it requires some con- 

 sideration to determine whether it ought to be buried in its com- 

 mon state, for in reality the greater part of the useful material of 

 the straw is a soluble silicate in this state and condition. Now if 

 the straw is burned, this operation renders the silica insoluble, at 

 least in a great degree; if on the contrary it is merely buried be- 

 neath the soil, where it will decompose, it will furnish its silica to 

 the succeeding crop of plants in a soluble condition. We may, 

 however, obviate the objection to burning by mixing with the ash 

 of the straw lime, by which the silica will become soluble again 

 and the potash of the straw set free, or be made available to the 

 uses of vegetation. 



The remarkable properties of silica or sand, or what in its pure 

 state is called quartz crystal, renders it a fit material to Ibrm the 

 basis upon which all our agricultural operations may be performed. 

 Its insolubility in its common form or state makes it a substantial 

 basis; and in its solubility in part when mixed or combined with an 

 alkali makes suitable material for entering into the formation of the 

 skeleton of the living plant. There are other properties which 

 it possesses, which fit it also for the functions which it fulfils as a 

 constituent of the soil, and as an element in the living organism 

 of the vegetable. 



We have many natural phenomena which prove and illustrate 

 the power of water to dissolve silica, especially when aided by 

 heat. The hot springs of Iceland deposit around them large 

 masses of nearly pure silex which had been dissolved in the water. 

 Even cold water, impregnated with carbonic acid, dissolves the 

 silicates. This has been shown by Polstorf and Weigmann. So 

 that by the quiet operation of water the silicates are dissolved. 

 The water in such a case contains silica, potash and soda, lime and 

 magnesia. From this experiment and from many observations 

 which have been made, it is satisfactorily shown that we are 

 greatly indebted to the influence of carbonic acid for the alkalies, 

 and pure or soluble silica in the soil. Anything, therefore, which 



