JoLY — 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 S23ecific 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 



IBANS. EOT. DUB. SOC, N.S., VOL. VH., PABT XTI. 2 N 



