METHOD OF SEPARATING THE CLAY AND SAND IN CLAY SOILS. 99 



with nearly all humus soils, heavy loams, and clays, the 

 soil is rubbed through by the fingers into a large basin with 

 the aid of water. After allowing the fine soil to settle for 

 half an hour, the supernatant turbid water is poured off, 

 the residue washed into an Erlenmeyer flask and boiled for 

 half an hour or more, according to the texture of the soil. 

 After cooling, the contents of the flask are removed to the 

 elutriator. A Scliultze's elutriating vessel of conical shape 

 is used, 3^ inches in diameter at top and 6 inches deep, 

 fitted with a brass rim, holder for funnel-tube, and overflow 

 tube. The water is allowed to flow from a reservoir by 

 means of a rubber tube delivering into a thistle-head tube, 

 15 in. long, leading down to half an inch of the bottom of 

 the vessel, where it is drawn out into a small orifice. The 

 rubber tube is about \ inch in diameter and provided with 

 a screw-clamp to regulate the flow so as to keep the thistle 

 tube full to the head. 



When the water from the overflow tube is quite limpid, 

 the clamp is screwed tight, the residual sand allowed to 

 settle, the water poured off, and the sand then washed out 

 into a basin and dried on the water-bath. This process 

 produces good results with sandy soils and light loams con- 

 taining up to about 30°/° of clay ; where, however, this 

 amount is exceeded, as a general rule the preliminary 

 treatment by boiling with water alone does not yield satis- 

 factory figures. To remedy this, several methods have 

 been used in order to more completely break up the clay 

 floccules into their constituent particles, of which perhaps 

 the most efficient is that of rubbing the soil in a mortar by 

 means of a caoutchouc pestle with a little water. 



The process is very tedious and there is a decided ten- 

 dency to underestimate the amount of sand present, owing 

 to the necessity of pouring off at intervals the clay in 

 suspension and adding fresh quantities of water. Scheme 



