6o 



RELATIONS OF SOIL TO WATER 



by different investigators are often not comparable. In some 

 methods the powdered soil is dried over sulphuric acid, or 

 at iooC.j and then placed in an atmosphere saturated with 

 water, and the gain in weight determined. Such a method 

 affords low results. In Hilgard's method the air-dried soil 

 is exposed to a saturated atmosphere at about 15 C., weighed, 

 and then dried at 200 C. This method will yield maximum 

 results, more of the colloid water being included. 



The following table will give a general idea of the absorp- 

 tive power of Mississippi and California soils for water- vapour 

 as determined by Hilgard and Loughridge (Portland Meeting, 

 American Ass. Advanc. Science, 1873; Rep. Agri. Expt. 

 Stations California, 1892-3-4, 70). In the rough classifica- 

 tion here adopted, a sandy soil contains less than 5 per cent, 

 of clay ; a sandy loam 5-10 per cent. ; a loam 10-15 per 

 cent. ; a clay loam 15-20 per cent. ; and a clay soil over 20 per 

 cent, of clay, as determined by Hilgard's method of mechanical 

 analysis (see p. 12). 



TABLE VI 



WATER EXPELLED AT 2OO C. FROM SOILS SATURATED WITH 

 WATER-VAPOUR, PER IOO OF DRY SOIL (HILGARD) 



This rough classification plainly shows that the power of 

 absorbing water- vapour is least in the case of sandy soils ; 



