216 IMBIBING POWERS OF SOIL. 



This number represents the mean specific gravity of the isolated 

 particles of the powder which has been examined. But we must 

 not from this density pretend to deduce the weight of a particular 

 volume of soil, a cubic foot or a cubic yard, for instance ; we should 

 come to far too high a number. The weight of a given volume of 

 earth must be determined immediately by ramming it into a mould 

 or measure of a known capacity. 



From M. Schiibler's experiments it appears, 1st. that silicious 

 and calcareous sandy soils are the heaviest of any ; 2d. that clayey 

 soils are of least density ; 3d. that humus or mould is of much 

 lower density than cKay ; 4th. that a compound soil being generally 

 by so much the heavier as it contains a larger proportion of sand, 

 and so much the lighter as it contains a larger quantity of clay, of 

 calcareous earth, and of humus, it is possible from the density of a 

 soil to infer the nature of the principles which prevail in it. In the 

 course of his experiments INI. Schiibier found that artificial mixtures 

 always gave higher densities than those that ought to have resulted 

 from the several densities of each of the sorts of substance which 

 formed the mixture. 



Imbibition of water. The power which soils possess of retaining 

 water or of resisting the too rapid dissipation of their moisture, is 

 highly important in its influence upon their fertility. This faculty 

 is measured comparatively in the following manner : a given quan- 

 tity of soil is taken, say from 3 to 400 grains ; it is dried until it 

 ceases to lose weight ; it is then made into a thin paste and thrown 

 upon a moistened filter ; when it has ceased to drop it is weighed. 

 The increase of weight is plainly due to the quantity of water re- 

 tained by the soil, thus : 



Weipht of the dr^- soil 300.0 



Weight of the moistened filler 75.0 



375.0 



Weight of the filter and moistened earth 525 



Water absorbed 150 



In the experiment quoted, 100 of dry earth absorbed or imbibed 

 50 of water. The following table contains the result of experi- 

 ments made on the imbibing power of diflJerent soils. 



Wftier abiorb«(] by 

 Kind of earth. 100 part* o( Um earth. 



Silicious sand 25 



Gypsum 27 



Calcareous sand 20 



Sandy clay 40 



Strong clay 50 



Sandy clay 70 



Fine calcareous earth 85 



Humus 190 



Garden earth 89 



An arable soil 5'.t 



.Another arable soil 48 



h appears, therefore, that the silicious and calcareous soils an<? 

 the gvpsum have the least aflinity for water ; the clayey soil re- 

 tained by so much the more as it contained a smaller quantity of 

 £:ui(i ; the fine calcareous earth retained 15 per cent. mor*f than the 



