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little or no water from air ; calcareous sand very little ; 

 ordinary arable, clay and humus soils, more and more. 

 Calcareous sand finely powdered absorbs 12 times as much 

 aqueous vapour as in coarse state. The rapidity of absorption 

 depends upon the proportion of moisture present in the air; 

 but the total amount of water absorbed mainly depends on 

 temperature, more being absorbed in low than in high tem- 

 perature. Hence the necessity of dessicating the soil in 

 uniformly high temperature for purposes of analysis. Sow- 

 ing of seed for Rabi crops should be done in the evening 

 after which the land should be harrowed and left in an open 

 state for absorption of dew. In the morning rolling or lad- 

 dering should be done so as to keep in the moisture absorb- 

 ed at night. 



87. Evaporation. Soils becoming superficially dry in day 

 time absorbs moisture at night. All soils exposed to air lose 

 their moisture more or less rapidly, sandy soils most rapidly, 

 clay less rapidly, and humus soils least rapidly. Exposed to 

 dry atmosphere at 19 C for 4 hours, 



Siliceous soil loses ... 88% of moisture. 



Calcareous sand ... 76,, 



Pure clay ... ... 52,, 



Clay soil ... ... ... 35,, 



Chalk ... .. 28,, 



Garden soil ... ... 24,, 



Humus or peaty soil ... 20,, 



88. Coagulation. In fresh water, clay remains in suspen- 

 sion for a very long time, but in salt water it gets coagulated 

 and deposited at the bottom. Hence formation of soils in the 

 sea is facilitated. The addition of common salt or gypsum 

 or of any soluble salt to a mixture of clay and fresh water 

 would demonstrate the action the sea has in the formation of 

 clay soils. The application of certain manures such as castor- 

 cake or gypsum to clay-soils, is known to make it more friable. 



89. Shrinkage and expansion. Pure clay contracts 18% 



