Joty—Some Sedimentation Experiments and Theories. 393 
The final disappearance of the upper boundary is thus not a suddenly 
attained state, but is reached by a gradual delay in the precipitation of the 
finer particles. This is also revealed in the fact that before final disappearance 
this boundary appears first at points which are ever lower in the tube and 
at stages in the settlement correspondingly advanced; also with increasing 
indistinctness. 
If a sediment which has settled under the action of a strongly concentrated 
salt be again shaken up, the phenomena first observed are repeated. There may 
be a small decrease in the rate of descent of the bounding surface. On again 
shaking up, the rate may show a further very small but distinct decrease. Finally 
the rate becomes apparently constant and a little less than the initial rate. 
If, however, the experiment of re-distributing a sediment be tried in the case 
of concentrations approximating to those which fail to produce a bounding 
surface, say to such as on first settlement leave the supernatant liquid so 
turbid as to give it a tallow-like opacity, then the interesting fact is revealed 
that on second or third shaking the boundary may utterly fail although distinctly 
produced on first settlement. There has, in fact, occurred some loss of effective- 
ness of the ions or change in the properties of the suspension, which forbids the 
repetition of the first effect. With each re-disturbance of the sediment the ionic 
action is less marked. Finally, the tube may be almost indistinguishable in its 
behaviour from one containing only silt and distilled water. 
Table I. contains experiments on the rate of falling of the sediment-surface in 
presence of a monad metallic ion at various concentrations, and after successive 
redistributions of the sediment. ‘The sign (?) indicates that no sediment-surface 
was distinguishable. It will be seen that at concentrations of 0-007 gram. 
equivs. per litre the obliteration of a surface of settlement occurred upon second 
and third settlements. 
[Taste I, 
2M 2 
