Cjo SOILS. 



atively short time obtains " clay " in which the upper limit of 

 size is one-half of that mentioned above, viz., .005 mm. But 

 for the costliness of the appliances required, including the 

 entire time of an operator, this method of separating the clay 

 would undoubtedly be preferable to the elimination by sub- 

 sidence; the more as a more minute grain-size for the clay 

 group is thus secured. 



The separation of the clay having been accomplished, the 

 various sizes of silt and sand may be separated by again sus- 

 pending them in water; and interrupting the settling process at 

 stated times, the grain-sizes corresponding to definite velocities 

 in settling may be segregated and weighed. When this process 

 of settling and decanting is carefully and repeatedly carried 

 out, very good results are obtained. 



Hydraulic Elutriation. The sedimentation (or 

 "beaker") method, long practiced in the arts is, 

 however, quite tedious, requiring the constant 

 close attention of a skilled observer. The desired 

 results may, in the writer's judgment, be more 

 conveniently obtained by the hydraulic method, 

 whenever no very large volume of work of this 

 kind is required to be done at once. 



When instead of allowing the soil to settle in 

 quiet water, the latter is used as an ascending cur- 

 rent of regularly graded velocities, it is clear that 

 the soil particles will be carried off by this current 

 in exact conformity with their several sizes (or 

 strictly speaking, volume-weights) ; and when 

 maintained in such a current for a sufficient length 

 of time, the entire quantity of the sediment cor- 

 responding to the prevailing velocity will be car- 

 ried away. It is of course easy to ascertain to 

 what grain-sizes certain velocities of the upward 

 Hotmtor. 8 ' current (regulated by a stopcock with arm moving 

 on a graduated scale) correspond, and to regulate accordingly 

 the intervals between the different velocities to greater or less 

 detail, as may be desired. A number of instruments have been 

 devised for this purpose, 



ScJwne's Elutriator is the one commonly used in Europe; 



