PROPERTIES OF DIFFERENT EARTHS. 35 



The absorbing powers possessed by the elements com- 

 posing a fertile soil, may be arranged in the following 

 order. 



Vegetable substances. 



Animal substances. 



Alumina. 



Carbonate of lime. 



Silica. 



Alumina, and those soils where its characteristics pre- 

 dominate, do not receive the moisture from the atmosphere 

 to the greatest advantage; they retain the water, which 

 they imbibe, with so much force, that the plants produced 

 upon them suffer as much from drought as if they grew 

 in sand. 



The light porous earths, composed of sand, carbonate 

 of lime, silica, and decomposed animal and vegetable sub- 

 stances, in just proportions, are the best for absorbing and 

 retaining moisture, in order to transmit it, with regularity 

 and beneficial effect, to the plant. 



The experiments conducted by Davy have produced re- 

 sults of great importance to agriculture ; he has compared 

 the energy with which various soils absorb humidity from 

 the atmosphere, and has uniformly found, that the most 

 fertile possessed this power in the highest degree ; so much 

 so, that the fertility of soils might be estimated, and class- 

 ed according to it. 



1,000 parts of a celebrated soil from Ormiston, in East- 

 Lothian, which contained more than half its weight of 

 finely divided matter, of which 11 parts were carbonate 

 of lime, and nine parts vegetable matter, when dried at a 

 temperature of 212° Fahr., gained in an hour by exposure 

 to an atmosphere saturated with moisture at a temperature 

 of 62°, 18 grs. in weight. 



1,000 parts of a very fertile soil, formed by the deposits 

 of the river Parret, in Somersetshire, gained 16 grs. 



1,000 parts of a soil from Mersey, in Essex gained 13 

 grs. 



1,000 grains of a fine sand from Essex gained 11 grs. 



1,000 grains of a coarse sand gained only 8 grs. 



1,000 grains of the soil from Bagshot-heath gained but 

 3 grs. 



The absorbing power of a soil has always been found 

 to be in proportion to its fertility, and to the excellence of 

 its situation. 



