APPLICATIONS OF THE VISCOMETRIC METHOD 289

fluidity-concentration curves linear?" and "Does the fluid 'soF
pass into the plastic 'gel' at a perfectly definite concentration and
temperature ? "

ArisJZ (1915) Las made a valuable study of the viscosity of a
10 per cent gelatine sol in a glycerol-water mixture of 1.175
specific gravity, with changing temperatures. Calculating the
fluidities, we obtain the linear curve

<p = 0.000227 (t - 45.2) (112)

which represents faithfully the observed values of the fluidities
given in Table LXXI. The temperature of zero fluidity is a
little over 45°, which must therefore be regarded as the transition
point between the fluid and solid phases, i.e., the melting-point.

TABLE LXXI.—THE FLUIDITIES OF 10 PER CENT GELATINE SOLUTION IN
GLYCEROL-WATER MIXTURE OP DIFFERENT TEMPERATURES (AFTER ARISZ)

Temp er atur e, degrees
Viscosity, observed
Fluidity, observed
Fluidity, calculated

44
30,000
0.000003
0.0000

46
5,000 ±
0.00020+
0.0002

47
4,200-
0. 00024 4-
0.0004

SO
950 ±
0. 00105 T
0.0011

55
415
0.0024
0.0022

65
222
0.0045
0.0045

In considering the effect of concentration on fluidity, we cite
first th.e data of Luers and Schneider (1920) on flour-water mix-
tures for 20°, giving the concentrations in volume percentages
(1006) and changing the viscosities to fluidities, Table LXXII.
The fluidities are again faithfully reproduced by means of a
linear formula, viz.,
<p = 100.5 - 569.66 (113)
except the last two concentrations, where the observed fluidity
is too high. This gives a concentration of zero fluidity as 17.6
per cent, which corresponds to the transition from viscous to
plastic flow. This is very close to the concentrations of zero
fluidity found by Bingham (1916) for clay suspensions, page 229.
10