292 E. W. Hilgard—Silt analysis of Soils and Clays. 
cal position. A very slight deviation from the vertical at once 
causes the formation of return currents, and hence of molecular 
the use of any water fit for drinking purposes are too slight to 
be perceptible, so long as no considerable development of the 
is all . Water containing 
the slimy fibrils of fungoid and moss prothallia, vorticelle, ete., 
will not only cause errors by obstructing the stopcock at low 
velocities; but these organisms will cause a coalescence of 
sediments that defies any ordinary churning, and completely 
4. The amount of sediment discharged at any one time must 
not exceed that producing a moderate turbidity. Whenever 
the discharge becomes so copious as to render the moving 
ixed character ; 
coarse grains being, apparently, upborne by the multitude of 
light ones whose hydraulic value lies considerably below the 
velocity used; while the churner also fails to resolve the 
This difficulty is especially apt to occur when too large 4 
quantity of material has been used for analysis, or when one 
sediment constitutes an unusually large portion of it. In either 
* Usually within 5 per cent of the quantities found. 
