SHRINKING OF SOILS. 219 



be tried and previously brought to the point of saturation with moist- 

 ure, was spread as evenly as possible. The weight of the disc 

 thus charged was noted, and it was weighed anew, after having 

 been kept for four hourc in a temperature of 18.75" cent. (65.75° 

 Fahr.) The weight of the water lost by evaporation was obtained 

 by a second weighing; the complete desiccation of the soil was then 

 completed in the stove. The following is the detail of one opera- 

 tion : 



Weight of the moist earth 310 



Weight after four hours' exposure to the air 260 



Water evaporated 50 



Weight of the moist earth 310 



Weight after complete desiccation 200 



Whole quantity of water contained in the soil tried ... 110 



Thus 100 of water of imbibition lost 45.5 during exposure to the 

 air for 4 hours at a temperature of about 66" Fahr. A more se- 

 verely accurate method might readily be contrived, but that employ- 

 ed by M. Schiibler appears sufficient for ordinary purposes. His 

 results, in regard to the different kinds of soil he tried, are these : 



100 parts of the water 

 cont:»ii)ed in the soil lose 

 Kinds of soil. in the course of 4 iioura 



at 66 (leg-. Fahr. 



Silicinus sand 88.4 



Calcareous sand 75.9 



Gypsum 71.7 



Sandy clay 52.0 



Stiffish clay 45.7 



Stiff clay •. 34.9 



"nrecUiy 31.9 



Calcareous soil 28.0 



Humus 20.5 



Garden earth 24.3 



Arable soil of Hoffwyll 32.0 



Arable soil of the Jura 40.1 



Of all the substances examined, sand and gypsum are obviously 

 those which allow the water to pass off most rapidly by evaporation. 

 The calcareous or chalky soil again has a high retentive power : 

 but it varies much in different instances, apparently in consequence 

 of different degrees of fineness ; it is however surpassed by humus, 

 and the garden soil which was tried. Humus is therefore at the 

 head of the list of substances in reference to retentive properties. 



All soils shrink more or less in drying, and form cracks, in the 

 way already indicated ; the shrinking has been estimated by means 

 of prisms of soils measured in the moist state, and after being dried 

 in the shade : 



Kinds of soil. 100 parts cube 



shrink to. 



Carbonate of lime in fine powder 950 



Sandy clay 940 



Stiffishclay 911 



Stiff clay 886 



Pure clay 817 



Humus 846 



Garden earth 851 



Arable soil of Hoffwyll 880 



Arable soil of Jura 905 



