84 THE PHYSICAL PROPERTIES OF SOILS 



SEVENTEENTH EXERCISE 



MECHANICAL ANALYSIS OF SOILS— CEN- 

 TRIFUGAL METHOD 



Make duplicate analyses of sandy loam and of clay 

 soil from the bins. Then, if time will permit, make 

 analyses of samples from the home farm. 



The method by which the separation is accomplished 

 is as follows: 



Take twenty to thirty grams of dry, pulverized soil, 

 mix thoroughly and dry in the oven. Cool in a des- 

 iccator, weigh out two 5-gram portions, transfer 

 one to an 8-ounce sterilizing bottle and the other to 

 a porcelain dish for ignition. 



Add to the sample in the sterilizing bottle about 

 150CC. of distilled water and ten drops of ammonium 

 hydrate to break up flocculation. (For the method of 

 preparing field samples see page 96.) Place the 

 bottle in a mechanical shaker and agitate until, when 

 viewed under the microscope, the soil particles are all 

 free from each other and present a clear-cut appear- 

 ance. Transfer the contents to the centrifugal test- 

 tube by means of a jet of distilled water. 



The separates to be determined are as follows : 



Fine gravel 2.0 — i.o mm 



Coarse sand i .0 — 0.5 



Medium sand 0.5 — 0.25 



Fine sand 0.25 — o. i 



Very fine sand o. i — 0.05 



Silt 0.05 — 0.005 " 



Clay 0.005 





