EXPERIMENT STATION BULLETINS. 



537 



FIG. 9. CURVES SHOWING EFFECT OF TEMPERATURE ON THE RETENTION OF 



WATER BY SOILS. 



greater portion of the water drained at the various temperatures, oc- 

 curred in the first few minutes when really the soil mass had not as yet 

 acquired to any appreciable degree the external temperature. Further- 

 more, if the soils were kept say at 50° C. for a considerable length of 

 time and the dripping of water had completely ceased the latter would 

 recommence almost instantly if the temperature was raised even 2 de- 

 grees higher. This observation seems to offer the real explanation as to 

 the cause of the diurnal fluctuation of ground water in shallow wells as 

 observed by King^^, and which has been erroneously attributed by many 

 writers to the diurnal change of the surface tension of the soil moisture. 

 There was probably air imprisoned within the soil between the surface 

 and the water level which contracted during the night and expanded 

 during the day and thus caused fluctuations in the ground water. 



In the case of the soils with large colloidal content some water is ac- 

 tually squeezed out at the maximum temperatures employed, due to ex- 

 pansion and swelling of the colloidal material. During preliminary tests 

 it was observed, for instance, that if peat and Clyde loam were in the 

 tubes in a rather compact form, water would be forced to the top at 

 the beginning, when the temperature was raised to 50° C. 



"U. S. Dept. of Agr., Bui. 5, Weather Bureau, pp. 59-Gl. 



