280

FLUIDITY AND PLASTICITY

'I,

nuwtnatcft In Relation, the location of transition points such as the
one* IwtwccHi NaaS(>4 and NaaSt^.lOHsO-1 Further work along
thinlino in zioodc.d to differentiate the effects of chemical com posi-
tion, ttMwtitution, and juwociation, inniHiiring the iluiditioH over a
ranfcfc of tcmpomturcH. AH in other linos of physical chemical
investigation, the* importance of making doterininatioiiH at more
than one temperature can hartlly be overestimated because
«ul)8tunc«H must be compared under conditions which are truly
coin parable*.
Various colloidal solutions Rueb as those of rubber, glue, •vis-
COHO, nitrocellulose,, dextrine*, gluten, et cet., offer problems of
importance which can bo most appropriately solved by the vi»-
tjornotcr. It is already known that the properties of a solution
of caoutchouc, for example, determine the character of the rubber
which can be* manufactured from it. The exact relation of the
viscosity of the HO! to the plasticity of the gel is practically a
dosed book. To indicate how complex the phenomena may be,
we may add that Carl Berquint of the Corn Products Refining
Company han found in an investigation of corn dextrines, tapioca
dextrine*, borax, gums and starches that as the percentage of
doctrine mereiweB during the process of conversion, the mobility
steadily risen whereas the* friction first falls, then rises, and again
falls/1 The quick netting of a gurn Boenw to bo associated with a
high friction. TliUH the addition of .25 per cent »odium hydrox-
ide to a 8.33 per cent Pearl starch reduced the mobility from
0.7214 to 0,3018 but increased the friction from 108 to 156 g
per square centimeter. The alkaline Hturch will set harder and
have "better body" than an acid starch.
Nitrocellulose Solutions.—The fluidities of nitrocellulose solu-
tions a« calculated from the determinations of Baker (1913)
would indicate that nitrocellulose solutions never become true
solids as the percentage of nitrocellulose in increased, for the
fluidities approach the ^ero value asymptotically. This con-
clusion is, however, so inherently improbable that it should be
confirmed. Since it was necessary to use a series of Ostwald
viecomoters in order to get the necessary range, and each one is
calibrated from another, the possibility of error is considerable.
*(?/. Dunfttan and Langton (1012).
•Privately communicated. Cf. Herschel and Bergquisfc (1921).