LABORATORY EXERCISES 



105 



40. Water Capacity of Soils. 



Materials. Air-dry sand, clay, loam, leaf-mold, or rotten manure, 

 spring-balance, four tin cans or paint-cans with holes punched in the 

 bottom, holes in the side, and string tied across for a bail. 



(a) Weigh each can. Fill two-thirds full, one with each of the three 

 soils, one with mixed clay and leaf-mold, one with mixed sand and leaf- 

 mold. Add water until thoroughly wet. Let this drain off for about 

 fifteen minutes. Weigh. 



The soil should be very dry before this experiment. It will still 

 contain some water, so that the results will all be too low. Why does 

 sand hold less water than clay? What effect on water capacity does 

 the addition of organic matter have? Notice that the organic matter 

 not only holds water on its surface, but all through it, like a piece of 

 bread that soaks up water. Give two ways in which a farmer might 

 increase the water-holding capacity of his soils. 



41. Capillary Rise of Water in Soils. 



Materials. Two small glass plates, three glass tubes three feet long, 

 one and one-half to two inches in* diameter, pan of water, cloth, and 

 sand, loam and clay. Three lamp chimneys may be used in place of 

 the glass tubes. 



(a) Fasten the two pieces of glass together by a rubber band- 

 Put a little splint at one side and set on edge in water. Notice that 

 the water rises between the plates and that it rises highest on the side 

 where the plates are nearest together. Make a drawing of this. 



(b) Put a piece of cloth over the end of each tube and fasten with 

 a rubber band or tie it on. Fill each with one of the soils. Set in the 

 pan of water. In which does the water rise most rapidly? Record the 

 results as follows: 



