THE .MECHANICAL ANALYSIS OF AUll) SOILS 



35 



thcro was usually an inert 



Fig. 3, — ilechanical Shaker for Soil Tubes 



'shaker' 



iniount of clay and this was taken to mean that thi.' 

 soil was being unduly broken down. Six hours 

 was therefoi-e taken as a sufficient length of 

 time to subject the soil to the action of the 

 shaker. 



The form of electrically-driven mechanical Mechanical 

 shaker adopted by the LI.H. Bui-eau of Soils is 

 shown in Fig. 3. At the time soil work was 

 begun in these laboratories a machine of this 

 type was not at hand, and the ordinary form of 

 end-over-end rotary shaker was used for the 

 purpose. The following results were obtained 

 on a sample of "cotton soil" known to contain 

 about 54; jier cent, of clay. Five grammes of 

 the soil were, in each case, treated with 75 c.c. 

 of water to which ten drojjs of strong ammonia 

 were added. For the sake of simplicity the 



proportion of clay only is given, though in many cases complete analyses were made. 



Later, a machine of the horizontal type was secured, and a short series of experiments 

 was carried out with it. These were not carried very far since it was soon evident that 

 vyhile the agitation was more violent, the results were not sufficiently improved to render 

 the method practicable. Thus : — 



The actual amount of clay present was, as in the former experiments, 54 per cent. 



The machine was run at the speed prescribed by the U.S. Bureau of Soils, 

 namely, 100 impulses per minute. By shaking more violently the amount of clay separated 

 in six hours was increased to 38' 2, a figure still far below the truth. 



As will be seen, even after 48 hours' shaking in the rotary machine, tlie proportion of 

 clay separated was only about two-thirds the total amount. 



