210

FLUIDITY AND PLASTICITY

is a sudden increase in volume and decrease in fluidity as shown
in Fig. 75 for p-azoxyanisole from the measurements of Eichwald
and Buhner. As the temperature is raised, the fluidity increases
in a nearly linear manner, passes through a sharp maximum,
and suddenly falls to the clarifying point, where there is a dis-
continuity in the curve. As the temperature is raised still
further, the fluidity again increases in a linear manner.
This behavior resembles that of molten sulfur which increases
in fluidity up to 150°, where the fluidity is 11.4 according to the
measurements of Rotinjanz (1908). It then suddenly falls off
to 0.0018 at 180° after which the fluidity gradually increases up
to 1.14 at 440°.
Drawing a parallelism between anistropic liquids and molten
sulfur, in no way explains the phenomenon, for the behavior of
sulfur is unexplained. Bose regards anistropic liquids merely as
emulsions of very long life. But an emulsion has invariably a
lower fluidity than a homogeneous solution at the same tempera-
ture, and according to the theory this must always be the case,
so that the emulsion theory seems to be excluded. The phenome-
non cannot be accounted for on the basis of the observed vol-
ume change, because the volume of the isotropic liquid is greater,
which would lead to an increase in the fluidity. We apparently
have but one explanation left, viz., that as the anistropic liquid is
heated to the clarifying point a new molecular arrangement is
formed which has a much larger limiting volume, so that although
the molecular volume is increased the free volume is lessened.
The same explanation would apply to sulfur.
Emulsions and Emulsion Colloids.—In our discussion of the
critical solution temperature, it was made clear that the separa-
, tion of the components of a mixture in the form of an emulsion
is attended by an increase in the viscosity. It seems probable
that this increase is due to the viscosities in emulsions being
additive, for it follows of necessity that when the viscosities
are additive the viscosity will be greater than in a homogeneous
mixture of the same composition. As in the case of suspensions,
there is considerable evidence that decreasing the size of particle
of the disperse phase brings about a corresponding decrease in the
fluidity. Martici (1907) experimented with oil-soap emulsions
and found that the fluidity becomes less as the drops become