240 



SOILS. 



From these figures it appears (1) that the greater part of the 

 vapor is condensed before the expiration of a single da^y, (2) that 

 humus is by far the most hygroscopic, but (3) that clay can ab- 

 sorb a large quantity of vapor. 



Temperature exerts a marked influence upon the capacity of 

 soils to absorb aqueous vapor, as is shown by Knop's exami- 

 nation l of a sandy and of a rich earth ; the amount of vapor 

 absorbed diminishes with elevation of temperature. 



645. The amount of liquid water which soils can absorb and re- 

 tain is verv different for different kinds of earth. In the follow- 



v 



ing determinations by Schiibeler dr}- soils were saturated with 

 water upon a funnel, and the increase of weight was noted after 

 all the excess of water had dripped away. The first column gives 

 the percentage of increase in weight of soil ; the second, the num- 

 ber of volumes of water that one hundred volumes of soil can take 

 up ; the third, the percentage of this water which evaporates from 

 the soil in four hours when it is spread over a given surface. 2 



640. The degree of fineness exerts also some influence upon 

 the absorptive power ; but while pulverization increases that 



1 Versuchs-Stationen, vi. , 1864, p. 281, where are found also some interesting 

 results recorded by Knop, in regard to the absorption of aqueous vapor by 

 various organic substances. 



2 Knop's Lehrbuch, 1868, vol. ii. p. 26. The third column is cited from 

 Johnson's "How Crops Feed," 1870, p. 180. 



3 Samples of peat have been known to absorb from 300 to more than 500 

 per cent of water. 



