THE PHYSICAL PEOPEETIES OF SOILS 95 



bottom will be deposited sooner than some of those of larger 

 size which have a greater distance to travel. If, however, 

 all the particles start from the top of a long column of 

 water at the same time, the largest will reach the bottom 

 first and the others after longer intervals according to size. 

 A method proposed by the author for the separation of par- 

 ticles in this way will be understood from the illustration 

 (Fig. 14). The apparatus consists simply of a pear-shaped 

 flask, about 200 c.c. capacity, w ( i,th a cylindrical neck about 

 100 c.m. long. The soil, thoroughly mixed with water, is 

 introduced into the flask, and the tube, after being filled up 

 to the top with water, is inverted over a pneumatic trough. 

 A small porcelain evaporating dish is placed under the 

 orifice of the tube so that the sediment may fall directly into 

 it. The dish is replaced by others at various intervals of 

 time so that groups of particles of different sizes may be 

 separately collected in them. 



The method of Bennigsen, of which the above is a modifi- 

 cation, is simpler, but it does not provide for the collection 

 of the separate groups of particles nor admit of their size 

 being mentioned. 



The micrometer used for measuring the size of the par- 

 ticles consists simply of a glass disc ruled in squares or, 

 more commonly, in simple divisions. It is introduced into 

 the eye-piece of the microscope so that the magnified par- 

 ticles and the divisions of the scale are seen at the safrne 

 time, as in Fig. 15. The size of the particles is then 

 easily read off. 



