120 



Physics of the Soil. 



The number of grains in one gram of each of these mix- 

 tures would be as given below : 



It is the custom to find the diameter of soil grains 

 either by direct measurement or else by counting and 

 weighing a given number of grains and then computing the 

 diameter of the mean grain from the weight and specific 

 gravity. If the diameter of the mean grain in the above 

 threo problems is computed by each of these methods the 

 results will be as below: 



If the surface of a gram of soil is computed /rom each 

 of these diameters the results given below will be found : 



These results are very different and differ so much from 

 the actual as to make them of little value in determining 

 the actual surface a given soil may possess. 



It has been the practice to take as the mean diameter 

 of the soil grain the average between the diameter of the 

 largest grain in the group and the smallest, which in the 

 above problem would give .004575 as the mean value. 



But to use this to compute the surface in a gram of soil 

 would give the results below: 



