Joty—Some Sedimentation Experiments and Theories. 401 
Many of the experimental facts are explicable on views now advocated. We 
find that the finest silts are the most resistant to flocculation. The failure of 
the ions to produce flocculation as the concentration is diminished is first shown 
in the continued suspension of the finer particles. Thus the overlying liquid 
grows gradually more turbid, with diminished concentrations. In the case of 
NaCl 0:225 gram. equivs. leaves a nearly limpid liquid; at 0°112 gram. equivs. 
the liquid is hazy; at 0-028 it is translucent only; at 0:014 it is nearly as 
opaque as tallow. In the case of a diad salt the same effect is noticed. 
MgCl,, traced from concentrations of 0:01 gram. equivs. downwards to 0:0008, 
gradually fails to clear down the finer sediment, leaving more and more in 
suspension, till finally surface is lost. Again, if the results of the present paper 
be compared with those obtained in the case of the much finer and more attenuated 
silts dealt with in my former experiments (loc. cit.), a similar law is found to 
obtain. The optimum in the case of the monad salt, NaCl, was near the point 
of saturation; in the case of MgCl, it was at about 0°032 gram. equivalents. 
This may be due, in the case of fine as well as attenuated suspensions, in 
part to comparative rarity of encounters under conditions suitable to the 
neutralization of repulsive forces and to the effectiveness of the expulsive 
forces in the medium. But generally the electrostatic properties of the silt 
will tend to retain ions of both signs upon the finest particles; probably there 
is quite an atmosphere of such ions around the particles, tending to check all 
close aggregation. It may, therefore, well be that the electrostatic properties 
to which we have referred may, in cases of extreme subdivision, actually retard 
the effectiveness of the expulsive forces arising from these properties. 
By re-shaking a precipitated sediment, we bring once more into suspension 
particles which are no longer at a marked negative potential. Linder and Picton 
have shown that ions, attaching themselves to minute colloidal particles, do so 
with such tenacity that even washing the precipitate with distilled water fails to 
remove them. We may, therefore, consider the actions which occur on second 
precipitation as almost uninfluenced by charges on the silt exerting attraction 
upon either ion. Evidently the clumping effects of the ions must now be mainly 
restricted to expulsive actions. When chance brings silt particles sufficiently into 
mutual approximation to establish a preponderating electrostatic effect urging 
them further together, this expulsive action of the ions will be available to forward 
the process of clumping. If the electrolyte is one of low concentration these 
actions may be feeble, without assistance from electric reactions between the silt 
and ions. The discharged silt exerts now no attraction upon the ions of either 
sign. It is probable, indeed, that the effects of increased ionic attraction across 
the silt medium is now most effective in securing adherence of ions of both signs 
upon the silt; and that herein is to be found another factor in delaying the 
clumping of a discharged silt. 
