On the Anahjsls of Soils. 27 



been just mentioned^ and partly upon some later improve- 

 ments. 



II. Of the Sulstances found in Soils. 

 The snbstances which are found in soils, are certain 

 mixtures or combinations of some of the prinutive earths, 

 animal and vegetable matter in a decomposing state, certam 

 saline compounds, and the oxide of iron. These bodies 

 alwavs retam water, and exist in very different proportions 

 in difterent lands ; and the end of analytical experiments is 

 the detection of their quantities and mode of union. 



The earths found in common soils are principally silex, or 

 the earth of flints, alumine, or the pure matter of clay, 

 lime, or calcareous earth, and magnesia. 



Silex, or the earth of flints, when perfectly pure, appears 

 in the form of a white powder, which is incombustible, 

 infusible, insoluble in water, and not acte^l upon by com- 

 mon acids J it is the substance which constitutes the prm- 

 cipai part of rock crystal ; it composes a considerable part 

 of hard gravelly soils, of hard sandy soils, and of hard 

 stony lands. 



Alumine, or pure clay, in its perfect state is white like 

 silex; it adheres stronglv to the tongue, is incombustible, 

 insoluble in water, but soKible in acids, and in fixed alka- 

 line menstrua. It abounds most in clayey soils and clayey 

 loams ; but even in the smallest particles of these soils it is 

 . usually united to silex and oxide of iron. 



Lime is the substance well known m its pure state under 

 the name of quicklime. It always exists in soils in com- 

 bination, and that principally with fixed air or carbonic 

 acid; when it is called carbonate of lime; a substance 

 which in the most compact form constitutes marble, and 

 in its looser form chalk. Lime, when combined with sul- 

 phuric acid (oil of vitriol), produces sulphate of lime 

 (gvpsuin), and with phosphoric acid, phosphate of lime. 

 The carbonate of lime, mixed with other substances, com- 

 poses chalky soils and marles, and it is found in soil sandy 

 soils. 



Magnesia, when pure, appears as white, and in a lighter 

 powder, than any of the other earths ; it is soluble in acid, 

 but not in alkaline menstrua ; it is rarely found in soils ; 

 when it does exist, it is either in combination with carbonic 

 acid, or with silex and alumine. 



Animal decomposing matter exists in very diflereut 

 slates, according as the substances from which it is pro- 

 duced are- diflcrt^it; it contains much carbonaceous sub- 



slanee. 



