Joty—Some Sedimentation Experiments and Theories. 399 
medium composing the silt at an increase of electric potential energy. The 
energy per unit volume of Faraday tubes being inversely as the specific inductive 
capacities of the two media, the ions supposed influencing one another across the 
matter of a silt flake will experience increased attraction. It is important to notice 
that this attractive effect will be greater for particles small enough to allow of close 
mutual approximation of the ions. In particles so large as to place the ions out 
of the sphere of mutual attraction the attractive effect on the negative ion will be 
nil. There are here forces tending to accelerate the attraction of positive ions 
to the particles of silt and to diminish the repulsion of negative ions. These 
forces do not exist for the larger particles. ‘Thus while there is co-operation 
among the forces attracting + ions; there is interference between forces acting 
upon the negative ions: the repulsive force acting most effectively in the case of 
the larger particles. There is, in fact, a preponderating tendency to bring the 
+ ions to the silt and more especially is this influence exerted in the case of larger 
silt particles, the attachment of negative ions being solely influenced by the 
establishment of lines of force in the medium of low specific inductive capacity. 
It may here be noted that, alongside of large particles, ions will not be attracted 
to the silt specially on account of the low specific inductive capacity of 
the silt: the lines of force will tend to remain in the medium of high specific 
inductive capacity: the effect in this case will be to increase the mutual 
attraction and mutual approximation of the ions, so that near the boundary 
between liquid and large silt particles there probably exists a layer in which 
re-combinations of ions occur more frequently than throughout the mass of the 
electrolyte. (It is probable, too, that this state of things exists at the free surface 
of electrolytes whether bounded by air or by glass, &c.) This greater frequency 
of re-combination, or greater amount of the un-ionised salt in the proximity of silt 
particles, does not probably influence the question of sedimentation or clumping 
of the particles. (It is probably a factor in the well-known ability of fine sands 
to extract salts from solutions. Indeed the increased electrostatic attraction 
arising in the low specific inductive capacity of sand or silt, and their de- 
ionising influence, are very certainly primary causes of this latter phenomenon. ) 
In order to perceive the bearing of the foregoing facts on sedimentation we 
must observe that these facts connote generally an expulsive action, exerted by 
the ions on the silt. Thus, wherever lines of force are refracted in or bent around 
silt particles, there is the tendency for those lines to straighten, and a lowering of 
electric potential energy in yielding to this tendency. If we now picture the silt 
particles brought by any means into close mutual approximation in the medium, 
this expulsive force tends to retain them in juxtaposition, the only condition being 
that the electric forces outside the clump of particles preponderate over those 
arising from ions entrapped between the particles. If the particles are so small 
as to approximate in dimensions to the average distance separating the ions, the 
TRANS. ROY. DUB. SOC., N.S., VOL. VII., PART XVI. 2N 
