PRACTICE XXI 



THE POWER OF COMPACT SOILS TO RETAIN 

 CAPILLARY WATER 



Use the five stock soils. 



Prepare the tubes in the same way as in Practice XX, but 

 compact the soil as directed in Practice XL Fill tubes to the 

 crease (except peat two-thirds full) and place in the same 

 galvanized-iron box with the tubes in Practice XX. 



Calculate the per cent of capillary water, the pounds of water 

 per cubic foot, and the acre inches of water retained. 



Which soil becomes wet on top first ? Why ? 



Which soil is drained first ? Why ? 



How does this correspond to total pore space ? 



How does rolling affect the water-holding capacity of a soil ? 



REFERENCES. 



Same as for Practice XX. 



" The Soil," Hall, pp. 105-107. 



44 



