88 SAND-WASTES OP FRANCE. 



These observations, I there stated, Marchand considered indi- 

 cative of the absorption of water being proportional to the state of 

 sub-division of the material composing the rock ; and this effect he 

 resolved into their hygroscopicity and their capillarity — the former, 

 the power of each molecule of the rock to retain around it a layer of 

 moisture difficult to withdraw — the latter, the property possessed by 

 many molecules of earth, to retain, in interstices by which they are 

 separated, small globules of water. 



From experiments and observations cited by Wessley, it appears 

 that, of all the constituents of soil, sand manifests the least capa- 

 bility of absorbing water into its composition. 



According to experiments by Schuebler, recorded in his Agriadtur- 

 Chemie (1830), a cubic metre of the following substance contained of 

 water the quantities stated : 



Kilogrammes. 

 Quartz sand, 499 



Pure grey clay, 875 



Fine carbonate of lime, 808 

 Humid acid, 935 



Field earth, 745 



Garden earth, 821 



The size of the grains of sand has an influence, and the capability 

 of absorbing moisture is increased with the fineness of the grains, — 

 but much more by the admixture of clay and lime, and most of all by 

 the addition of humid acid. 



Pure quartz sand has no power of attracting moisture from the 

 atmosphere, but it gains this power by the admixture of other sub- 

 stances ; and the operation is promoted by the reduction of the size 

 of the grains. 



According to statements in Heyer's Forstliche Bodenhunde, founded 

 on investigations by Schuebler, 5 grammes of the following sub- 

 stances spread out over 360 square centimetres, attracted from the 

 air in 72 hours the affixed number of centi-grammes ; and the pro- 

 portions would have been the same whatever weight had been taken : 

 Pure quartz sand, ... ... ... 0"0 



Pure grey clay, ... ... ... 24"5 



Powdered carbonate of lime, ... ... 17"5 



Humid acid, ... ... ... 60* 



Field earth, ... ... ... 11-6 



Garden earth, ... ... ... 26* 



