POWER OF RETAINING WATER 75 



then, when dropping has ceased, three layers may be dis- 

 tinguished, but the divisions are not marked with the sharpness 

 that appeared in the former case. The lowest layer as before 

 is fully saturated, and the highest layer is fully drained, and 

 contains a uniform proportion of water, but there lies between 

 them an intermediate layer, often of considerable length, in 

 which the proportion of water is not uniform but increases 

 from above downwards till it merges into the full water 

 contents of the lowest layer. In this case, the water in the 

 fully drained layer not only coats the particles, but fills the 

 finest of the interspaces. In the intermediate layer, more and 

 more of the interspaces are occupied with water as the sand 

 gets nearer the bottom, till at last the largest are occupied, 

 and the sand is found completely saturated. 



If, in a third case, the tube is filled with an extremely fine 

 powder, firmly packed together, and then saturated with water, 

 this powder may be found to exhibit no loss by drainage, but 

 the tube remains filled throughout with matter of one uniform 

 degree of wetness. In this case the interspaces are so fine that 

 the water filling them is held too firmly to obey the force of 

 gravity. The cause of these various results will be better 

 understood when we have discussed the subject of capillary 

 action. 



Schlibler made many experiments on the power of various 

 soils to retain water, but his results, and those of other early 

 investigators, are generally too high, the experiments being 

 made in short tubes or funnels in which the soils were never 

 thoroughly drained. A. Mayer has made use of a tube i metre 

 long, composed of two pieces joined by caoutchouc, the upper 

 piece 25 cm., the lower 75 cm. in length. The tube is filled 

 with powdered soil, which is then saturated with water. When 



