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202

FLUIDITY AND PLASTICITY

shown in Fig. 73, for English china clay and water. This concentra-
tion of zero fluidity is independent of the temperature and is the
concentration which serves to demarcate viscous from plastic flow.

Volume percentage Clay

FIG. 73.—Tlie fluidity of aqueous suspensions of clay in water according
to measurements of Durham.

We are not to conceive of a suspension of zero fluidity or infinite
viscosity as incapable of being deformed, but it would not be per-
manently deformed by a very small shearing force. It remains
an important question which we are unable to answer positively