LABORATORY PRACTICE 



317 



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 sepa- 

 rations are reasonably com- 

 plete. The sediment in the 

 cylinder consists mainly of 

 silt. The fine particles which 

 remain suspended in the water 

 of the cylinder and cause the 

 roiled appearance are mainly 

 the clay particles. In this 

 experiment note approxi- 

 mately what grades of soil 

 particles predominate in your 

 soil. Save the liquid in the 

 cylinder for the next experi- 

 ment. 



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 0.5 



gm. calcium hydroxide and F IG. 58. Movement of Water through Soils, 

 stir. To beaker No. 2, add 



i gm. of calcium hydroxide and stir. The third beaker is used for 

 purposes of comparison and no calcium hydroxide is added. After 

 24 hours examine the three beakers and note the influence of the 

 calcium hydroxide in precipitating the clay and clarifying the liquid. 



