COLLOIDAL SOLUTIONS

205

The curves of infusorial earth in water, page 55, are convex up-
ward at the lower temperatures and convex downward at the
higher temperatures. The explanation of this behavior is not
known. Plotting the fluidities and concentrations of " night
blue" studied by Biltz and Vegesack (1910) we find that all of
those curves are convex upward, the zero of fluidity being at

TABLE LV.—FLUIDITIES OF SUSPENSIONS OF TRINIDAD LAKE ASPHALT
IN BENZENE AT ABOUT 20° (AFTER C. RICHARDSON)

Per cent asphalt by weight
Per cent colloid in asphalt
Fluidity observed
Fluidity calculated c = 34.5 weight per cent

0

153.0

1
2.54
353.0
149

2
2.01
146.0
144

5
2.09
132.0
131

10
2.73
104.0
109

20
3.13
61.0
64

30
4.19
24.0
20

40
6.51
11.0
13

50
10.69
3.1

about 9.2 weight per cent. Allowing the suspensions to stand
for several days causes a marked decrease in the fluidity as does
also the purification of the material.
Woudstra (1908) investigated colloidal silver solutions. In a
solution containing only 0.0046 per cent silver by volume,
the fluidity at 26° was lowered 4.3 per cent so that it seems
possible that a solution containing less than 1 per cent of silver
would have zero fluidity! The data are too scanty to permit
an exact estimation of the zero fluidity concentration and the
fluidity-volume concentration curve is highly convex upward.
With the elapse of time and under the influence of electrolytes
colloidal silver solutions coagulate and there is a simultaneous
increase in the fluidity. This is in accordance with our other
knowledge of the effect of size of particle but it is in marked
contrast to the effect of "setting" on the fluidity of the polar
type of colloids.