98 L. COHEN. 



A METHOD of SEPARATING the CLAY and SAND 



in CLAY SOILS, AND THOSE RICH in ORGANIC 



MATTER. 



By L. Cohen, Chemical Laboratory, Department of 



Agricu] ture. 



(Communicated by F. B. Guthrie, f.i.c, f.cs.) 



[Read before the Royal Society of N. S. Wales, December 6, 1905.~] 



Considerable difficulty has always been experienced in 

 effecting the complete separation of the clay and sand 

 fractions of those soils that contain above the average 

 either of clay or organic matter. The chief obstacle to an 

 exact mechanical analysis of the fine soil appears to be 

 that the particles of clay form themselves into aggregates, 

 very often having a minute vegetable fibre as a nucleus, 

 and these aggregates behave in the elutriator as though 

 they were sand grains of the same dimensions. This 

 property possessed by organic matter or humus of cement- 

 ing together the clay particles, though rendering, as a rule, 

 the texture of the clay soils (in situ) more open, interferes 

 considerably with the correct estimation of the constituent 

 particles of the soil. 



The method of preparation of a sample of soil usually 

 employed in order to separate the clay by the action of a 

 moving current of water is as follows : — A weighed portion 

 is passed through a sieve which retains the stones, coarser 

 root fibres, and gravel, and the fine soil is boiled with water 

 until the clay particles are completely separated from the 

 sand, and the floccules broken up. In this laboratory the 

 sieve used allows all particles to pass through of a diameter 

 of A- of an inch or less. If necessary, and this is the case 



