EXPERIMENTS 267 



tar, and about 20 cc. of water added. The soil is pestled with a 

 rubber tipped pestle with the object of separating adhering parti- 

 cles without pulverizing the individual soil grains. After two or 

 three minutes rubbing, more water is added and the soil and water 

 are allowed to sediment for about one minute ; the turbid liquid is 

 then decanted into a beaker. This process of soft pestling and 

 decantation is repeated two or three times until the remaining soil 

 grains appear free from adhering smaller particles. With some 

 soils this is a tedious process. The contents of the mortar are then 

 transferred to the beaker and enough water is added to nearly fill 

 the beaker. The contents of the beaker are thoroughly stirred, 

 and after three to five minutes sedimentation, the turbid liquid is 

 decanted into a second beaker leaving the sediment in the first 

 beaker. More water is added to the first beaker and the process 

 of stirring, sedimentation and decantation are repeated until the 

 sediment consists mainly of clean and fine sand. The turbid liquid 

 in the second beaker is decanted into a large cylinder ; the sedi- 

 ment in the second being washed with more water and the wash- 

 ing added to the cylinder. It is to be noted that the sediment in 

 the second beaker is composed of finer particles than the sediment 

 in the first beaker. The sediment in the first beaker consists 

 mainly of medium and fine sand, and in the second beaker, of fine 

 sand and coarse silt. Some sand particles are carried along in the 

 washings into the large cylinder. It is difficult to make even an 

 approximate separation of a soil into sand, silt and clay particles. 

 In the mechanical analysis of soil, the chemist uses the microscope 

 to determine when the separations are reasonably complete. The 

 sediment in the cylinder consists mainly of silt. The fine parti- 

 cles which remain suspended in the water of the cylinder and 

 cause the roiled appearance are mainly the clay particles. In this 

 experiment note approximately what grades of soil particles pre- 

 dominate in your soil. Save the liquid in the cylinder for the next 

 experiment. 



Experiment No. 10. 

 Sedimentation of Clay. 



In each of three separate cylinders or beakers place 200 cc. of the 

 turbid liquid saved from Experiment No. 9. To beaker No. I, add 

 .5 gm. calcium hydroxid and stir. To beaker No. 2, add i gm. 

 of calcium hydroxid and stir. The third beaker is used for pur- 



