LE. W. Hilgard—Flocculation of Particles. 205 
Art. XXIV.—On the Flocculation of Particles, and its Physical 
and Technicul Bearings; by EUGENE W. H1ucGarp, of the 
University of California, 
according to the circumstances of temperature and moisture. 
me discussions since made, and more especially that of Pro- 
fessor S. W. Johnson, on the Mechanical Effects of Tillage,* 
appear to me to render desirable a more detailed consideration 
of the various bearings of this phenomenon, which, despite its 
simplicity, and obviousness in every-day life, seems _not to 
have received all the attention it deserves. This is strikingly 
exemplified in the modes of experimentation and the more or 
less contradictory results obtained by different observers—Von 
enze, Haberlandt, Ad. Mayer, Nessler, and others who have 
studied the capillary relations of soils to water. In comparing 
the effects of “packing” and “loosening” of powders and 
soils upon their relations to water, it makes a material differ- 
ence whether the material used was dry, damp or wet, an 
whether or not the soil had been previously under tillage for 
some length of time. Again, Johnson seems to incline to 
attribute to the flocculation of the clay in soils, by various 
agencies, effects which, I think, clearly belong to all small par- 
ticles as such. : 
Perhaps the best fundamental experiment (which can be 
neatly projected on a screen by the beam of a magic lantern) is 
the one described in my previous paper (loc. cit., p. 290). 
of 1™™" per second, is introduced into an ordinary conic-cylin- 
drical elutriating tube, placed vertically, in which the current 
of water entering at the small orifice below, alone performs the 
stirring-up needed to keep the sediment from settling down. 
a current of water be turned on, corresponding to a 
Velocity below that of 1™™ at the mouth of the tube, of course 
none of the sediment can pass out of the upper end, but it will 
be kept circulating in the conical portion, by a current going 
upward in the axis of the tube, and downward on the sloping 
sides of the cone. If this be kept up for ten or fifteen min- 
utes, and then the velocity gradually increased, it will be found 
that scarcely any of the sediment will pass off, either at the 
* Rep. Conn. Exp. Station for 1877. 
