204 GEOLOGY AND CHEMISTRY OF SOILS. 



cimen, and you may sum up your results, and see liow nearly 

 ' they will balance, and if there is a loss, you must make another 

 examination for salts of potash and soda, in the manner I shall 

 give presently. Let us first sum up the above operations. 



A Water of absorption. 



B Organic matter. 



C Insoluble silicates. 



D Per-oxide of iron. 



E Alumina. 



F Lime. 



G Magnesia. 



H Manganese. 

 In order to ascertain the existence of alkaline salts, burn off 

 the vegetable matter from another 100 grains of the dry soil. 

 Then pour over it a little nitric acid, and digest it at a boiling 

 heat. Dilute and filter the solution, evaporate it to entire dry- 

 ness, fiise the saline matter obtained, and drop into it a few 

 fragments of prepared pure charcoal. If nitrates are present, 

 deflagration will take place, and the alkaline bases will be con- 

 verted into carbonates. Dissolve the residue and test a drop 

 of the solution by means of a solution of chloride of platina and 

 soda. If potash is present, a yellow powder will precipitate, 

 but none will fall if soda alone is present. 



Sect. 2. Composition of Soils as cUter mined hy Analysis. 

 The composition of soils might generally be deduced from 

 the composition of the rocks out of which they are formed, 

 provided no chemical nor mechanical changes were wrought 

 upon them in the process of disintegration. But as the 

 proportion of the ingredients are changed in this process, 

 as some of the alkalies are abstracted by growing plants, or 

 removed by successive crops, and as organic matters are 

 added, we must resort to an examination by analysis, in or- 

 der to ascertain the exact composition of any soil which is 

 presented for our inspection. By this examination, soils are 

 found to be composed of two parts: 1. the mineral ingredi- 

 ents, or inorganic portions, which include the alkalies, metal- 

 lic oxides, salts and earths ; 2. the vegetable and animal 



