92 SOILS AND MANURES 



have been proposed for the purpose, some of them 

 aiming at greater accuracy than others, but they all belong 

 to one or other of two types. In one case the separation 

 is effected by the movement of a current of water, and in 

 the other by the subsidence of the particles through a 

 column of water at rest. 



Schone's method is, perhaps, the best of those which 

 depend upon the motion of the water. The principle will 

 be readily understood from the illustration of the appara- 

 tus (Fig. 13). The soil is placed in the elutriator c; a 

 current of water passed through it, from below upwards, 

 carries off all the particles of a certain size, corresponding 

 to the velocity, and is collected in the beaker e. The water 

 is supplied from the reservoir a; the velocity of the current 

 is regulated by the level of the water in the cylindrical tube 

 fc, and is measured by the height to which the water rises in 

 the piezometer d. When all the particles in the first group 

 have been carried over, the beaker e is replaced by another, 

 the speed of the current is increased and a second group, 

 consisting of particles of larger size, is obtained. After 

 that, a third group, a fourth group and so on are obtained 

 in the same way. The size of the particles in each group 

 depends upon the velocity of the current, or hydraulic 

 value as it is called, and it has been shown that the 

 observed and theoretical values correspond very closely. 

 Hence, if the speed of the current is accurately known, the 

 size of the particles in each group can be calculated and 

 does not require to be measured. 



The table on p. 93 shows the hydraulic values of the 

 particles of different sizes. 



Osborne's is perhaps the best known method for the 

 separation of the particles jby subsidence. Briefly out- 

 lined it is as follows : 



A quantity of soil is thoroughly disintegrated and stirred 

 with water. When the liquid comes to rest the larger 



