238 



ROCKS AND SOIL 



cheesecloth over the lower end of each chimney. Invert them and 

 pour in -J- pint of water on the soil in each. Catch the liquid that 

 passes through and measure it. Which soil holds water best? 



Water and Air in the Soil. You are all familiar with 

 the fact that coffee creeps up on a lump of sugar placed 

 partly in it, and that oil rises in a lamp wick. You may 

 wish to try the experiment on capillarity described below. 



Have four very fine tubes, 

 each having a different 

 hole of different diameter 

 running through them. 

 These are placed side by 

 side in a dish of water. 

 The smaller the diameter 

 of the tube, the higher 

 the water will rise in it. 

 This rise of fluids against 

 the force of gravity is 

 called capillarity. Soil, 

 if examined under a mag- 

 nifying glass, is found to 

 be made up of many par- 

 ticles of different sizes, 

 each particle holding 

 around it a film of water, 

 as shown in the diagram. 

 Water rises through the 



Each particle of soil is surrounded by a 

 film of water and air spaces are found 

 between the particles. The artist has ex- 

 aggerated these to show how air and water 

 are held in the soil. 



