Joty— The Inner Mechanism of Sedimentation. 329 
sediments will conform to the square and cube law, the element 
of probability fuily entering, even at considerable concentra- 
tions.' 
The actual results as observed in the rates of clearing of 
suspensions in more concentrated solutions will be compli- 
eated by the influence of viscosity and specific gravity ; and 
experiments will be further exposed to the disturbing effects 
of thermal convective currents, which are difficult to eliminate 
entirely. 
The method of experiment is to produce fine suspensions by 
- allowing the settlement of various finely powdered substances, 
such as carbon, kaolin, quartz, obsidian, basalt, &e., to proceed in 
distilled water for a few hours or days, and finally to pour off 
the upper portion for use. ‘This is now diluted to a strongly opa- 
lescent liquid and exposed to the action of the salts, under con- 
ditions of perfect stillness and as nearly uniform temperature as 
possible. About 100 c.cs., contained in a wide test-tube, is sufficient 
liquid to deal with. ‘The tubes are placed side by side, immersed 
in a tank of water having glass sides, and viewed against a black 
background by light which enters from behind and from above, 
and which should be uniformly intense for all tubes being com- 
pared. The tubes are supported by attachment in a board covering 
the tank, in which holes to receive the tubes are made closely 
adjoining. 
The following are the principal experimental results dealing 
1The obscure phenomena of pedesis may find an explanation in the facts attending 
flocculation. There are, in all cases, along with the visible pedetic particles, necessarily 
large numbers of sub-microscopical particles present. The larger particles which are 
not discharged are unstable in the presence of these smaller particles ; for any move- 
ment of the larger particles is attended with disturbance in the symmetry of its 
electrical layer, the forward side becoming more discharged than the rear side owing to 
the larger number of ionic encounters on the side of advance. Repulsions, due to 
mutual electrification, may now exist on the rear side, while attractions between the 
discharged surface and small electrified particles may operate on the forward side. 
Thus, the pedetic motion is the result of the diffusion throughout the liquid of electrified 
particles and ions, and derives its energy from the electric potential consequent on 
this distribution. In pedesis we see the process of flocculation in progress. In “ pure ”’ 
water the motion may persist for an indefinite time, for after a certain degree of growth 
the aggregates may become detached from the larger particle and break up by 
mutual repulsion. If ions are abundantly present, this break-up does not happen, 
discharge being complete, and sedimentation ensues. 
