APPLICATIONS OF THE VISCOMETRIC METHOD 281

So it may well be that nitrocellulose solutions in various non-
aqueous solvents may be brought into line with other colloidal
solutions, some of which have already been considered, page 198.
If, for a given nitrocellulose, there is a zero of fluidity which is
independent of the particular solvent, an empirical formula of
the general type

where K is a constant, may be serviceable, (cf. Duclaux and
Wollman (1920)).
Colloidal solutions of the above types which have a lattice-
work or sponge-like structure show an increase in the fluidity
when subjected to treatment which breaks up this structure.
Astonishingly small quantities of the disperse phase are necessary
to give zero fluidity or at any rate a very great viscosity.
Certain non-polar emulsion colloids, such as milk, are in some-
what sharp contrast with the above, because fairly high percent-
ages of the disperse phase alter comparatively little the fluidity
of the medium and the reduction of the size of the fat gluobles it
by "homogenizing" decreases the fluidity.
Attempts are being made to use the plasticity method in the
study and control of butter and other fats and greases. As a
means for distinguishing between different fats and greases and I f
of determining the amount of the "hardening" of oils in the proc-
ess of hydrogenation, or of oxidation in the blowing of oils, the
method offers opportunities which have not been exploited as
yet. Similarly it seems practicable to estimate the amount or
quality of gluten in samples of flour by this method.
Clay and Lime.—Suspension colloids offer a simpler set of
conditions than can be found anywhere else. Clays, plasters,
mortars, and cements, are all plastic and their plasticity is a
matter of prime importance in their respective industries.
Commenting on the influence the plasticity of plaster has on its
economic usefulness, Emley (1920) states that about 70 per cent
of the total cost of plastering a house is accounted for in the
labor required to spread the plaster. "If one plaster is more
plastic than another, it means that the plasterer can cover more
square yards in a given time with the former than with the latter,
which, of course, will reduce the cost. Furthermore the more