COLLOIDAL SOLUTIONS

203

as yet, whether the viscosity of a suspension is independent of the
instrument in which the measurement is made or not. It seems
a necessary conclusion that the concentration of zero fluidity
must be determined in a long, narrow capillary. The fluidities of
suspensions follow the empirical formula

(71)

in which 6 is the volume concentration of the solid and c is the
particular value of b at which the fluidity of the suspension
becomes zero. The value of c can vary only from 0 to 1, the
value increasing with the size of the particles. This equation
closely resembles Eq. (70) and becomes identical with Eq. (69)
when c = 1.

In Table LIV the fluidities of graphite suspensions are compared

TABLE LIV.—THE FLUIDITIES OF SUSPENSIONS OF GEAPHITE IN WATER
AT DIFFERENT TEMPERATURES, (AFTER BINGHAM AND DURHAM)

C = 5.4 PER CENT

Temperature, degrees
Volume percentage, graphite
Fluidity observed
Fluidity calculated
Volume percentage, graphite
Fluidity observed
Fluidity calculated

30
0.396
116.8
115.7
.048
100.9
100.7

35
0.395
129.8
128.3
.046
113.4
111.7

45
0.394
156.3
154.8
.042
135.0
134.8

55
0.392
184.9
183.0
.037
161.7
159.5

65
0.390
215.5
213.1
.032
192.1
185.7

with the values calculated by formula (71). The two agree
extremely well, which may be due to the fact that the graphite
suspensions (aquadag) are very stable, obviating trouble due to
settling out and clogging the capillary. That the subdivision
of the graphite is carried very far is indicated by the very low
value of the concentration of zero fluidity, c = 5.4 volume per
cent.
Some of the suspensions of sulfur by Oden (1912) are plotted
in Fig. 74 using volume percentages, taking 1.90 as the specific
gravity of sulfur. These values indicate a zero of fluidity at
about a 25 volume per cent suspension. Some of the values are
not on the curves, particularly at the high concentrations; but the