MANUAL OF GENERAL AGRICULTURE. 19 



17. ONE EFFECT OF HUMUS, OF SAND, AND OF 



LIME, ON A CLAY SOIL. 



Materials: Four pans, clay, slaked lime, sand. 



Fill four pans i/4 full of clay and treat as follows : 



To the first add enough water to saturate the clay. 

 Make a note of the amount of water used. 



To the second add about l /2 its volume of humus or 

 fine, dry, well-rotted manure, and the same amount of 

 water as before. 



To the third add *4 its volume of slaked lime and 

 water, the same as before. 



To the fourth add % its volume of sand and the same 

 amount of water as before. Make each into a ball and set 

 aside to dry. In a few days examine and see which one 

 can be more easily pulverized with the fingers. 



Questions: 1. State the conclusions as to the value 

 of humus, sand, and lime on a clay soil as shown in this 

 experiment. 2. What causes a clay soil to bake. 3. 

 How can the baking of a clay soil be prevented ? 



18. DETERMINATION OF THE SPECIFIC GRAVITY 



OF SOILS. 



Materials: Graduated cylinder (25 cc. or 50 cc.), 

 sand, clay and loam soils. 



In this experiment we are to compare the weights of 

 different soils with the weights of equal volumes of water. 

 Ascertain the weight of 10 cc. of water. Place exactly 

 10 cc. of water in the cylinder, reading to the top of the 

 column but not including the crescent formed on the sur- 

 face of the column. This water crescent is called the ' * men- 

 iscus." Pour 10 grams of accurately-weighed sand which 

 has been dried to a constant weight into the water. Shake 

 to expel the air. Take the reading as before, not includ- 

 ing the meniscus. Subtract 10 from this reading, and the 

 remainder is the volume of water displaced by the sand. 

 Determine the weight of displaced water and calculate the 

 specific gravity according to the following formula: 



Wt S. 

 Sp.= - 



wt. w. 



