396 Joty—Some Sedimentation Experiments and Theories. 
so that all in the one group received the same amount of agitation when 
the sediments were being distributed and re-distributed throughout the liquid, 
and were approximately at the same temperature. The test tubes were selected 
to be as closely as possible of the same dimensions. 
To what is the remarkable change appearing on re-disturbance of the sediment 
to be ascribed ? To an abstraction of ions from the solution by the silt or to some 
physical change in the silt. The first explanation seems @ prior’ most probable... 
To investigate the matter I decanted the over-lying liquid from tubes 
containing sediments which had experienced frequent disturbance till all 
surface during settlement was lost, till sufficient was got to apply the 
liquid to fresh silt, not before used. All quantities and conditions being 
alike with those obtaining in the first experiments, it was now found that this 
solution was just as vigorous as it was upon the occasion of the first usage; 
revealing a distinct boundary surface to the descending silt and the same 
turbidity above. On re-disturbing those new tubes they gradually, on the second 
_ or third precipitation, lost their bounding surfaces just as in the case of the first 
use of the solution. ‘This experiment being several times repeated with the 
same results, leaves no room to suppose that any appreciable change in the 
solution is responsible for the effects noticed. 
The next step was to examine the sediment. The “ ineffective” sediment, 
as for brevity I will call that which has lost the property of revealing a bounding 
surface during descent, left behind in the tubes which furnished the used solu- 
tion for the last experiments was supplied with fresh solution, the concentration 
of which was the same as at first used. It was now found that the loss of surface 
persisted. The fresh solution left the appearance quite unchanged. In fact it 
it is evident that to some change in the properties of the sediment the effect 
observed is to be ascribed. 
Experiments were now made to try if increased concentrations of the 
ions would not restore the surface to the ‘ ineffective” sediment. It was 
found that increased concentration had this effect. Thus silt which had lost 
surface by re-disturbance in a 0:005 gramme-equivalent solution of NaCl 
recovered it first in a solution of 0°010 gramme-equivalents and one which 
in 0:00083 gramme-equivalents of MgCl, had lost surface regained it first visibly 
in a solution of 0:00111 gramme-equivalents of the same salt. 
The experiments referred to may be summarised as follows :— 
On the Electrolyte. 
NaCl 0:005. 12 c.cs. which had become ineffective with 5 grams. silt were withdrawn, and 5 grams. fresh 
silt added. Well-defined surface : depression in 10 mins. 1:8 cms., in 30 mins. 4°8 cms. 
Second settlement, some surface still produced. 
Third settlement, surface almost indistinguishable. 
