288

FLUIDITY AND PLASTICITY

molten metal. Feild (1918) has investigated the viscosity of
slags.
The sodium silicate used in industry contains varying hydroxyl
ion concentration. An excess of silicic acid increases the adhes-
iveness but lowers the mobility. Excess of alkali has the opposite
effect. The alkalinity of sodium silicate is therefore obviously
an important control factor.
Conclusion.—If one plots the viscosity-concentration curves
of a colloid sol of the type of gelatine in water or of nitrocellulose
in acetone, one finds that the viscosity rapidly goes from the
very small viscosity of the pure solvent (O.Olp for water at 20°
and 0.003 for acetone at 25°) to an extremely high value which
may be regarded as infinite, in a concentration of only a few per
cent. Plotting these curves leads to unsatisfactory results,
which need not be exhibited here as they are very common in the
literature; the curves fall together at one extreme as soon as one
tries to represent more than the most dilute solutions, and where-
as they may or may not coincide at the other extreme, we can
form no idea of what happens since that extreme is infinitely
removed from us.
If however we plot fluidities instead of viscosities the whole
problem becomes immediately simplified, for the fluidities of the
pure solvents assume their proper importance and the fluidity
goes to or, at any rate, approaches zero, which is accessible.
Moreover the concentration of zero fluidity has a definite and
important significance. If the relation turns out to be also
linear, then the problem is one of ideal simplicity.
To go over all of the data in the literature, critically examining
the data to see how far it could be used to support and further
amplify the theories set forth in this work has been a pleasant
task but far too great for a single worker. Already several
workers are in the field and in the Index and Appendix I are
bringing together a considerable number of references and tables
in order to facilitate the work.
A consideration of the following data may aid any who are
interested hi the theoretical study of colloids or in their industrial
applications, since they help us to answer the very important and
novel questions: "Are fluidity-temperature curves linear in the
case of emulsoid colloids of the type of gelatine?" "Are their