VISCOSITY AND FLUIDITY 95
nahme im kiitischen Gebiete und stehen rnit einander in einem
innigen Zusammenhange." Friedlander also observed that the
expansion coefficient and the coefficient of electrical conductivity
as well as the refractive index remained normal. He believed
that it was necessary to go farther than had Ostwald and Stebutt
in order to reach an explanation, and that a definite radius of
curvature of the separating surfaces must correspond to each
temperature, otherwise the degree of opalescence could not be
definitely determined. He therefore attributed the increase in
viscosity to the formation of drops, but he was puzzled by the
fact that when a solution of colophonium in alcohol is poured into
a large quantity of water, a highly opalescent liquid is obtained
which has, nevertheless, practically the same viscosity as pure
water. This theory of Friedlander is apparently an outgrowth
of the theory of "halbbegrenzte Tropfen" of Lehrnann. Fried-
lander also discussed the electrical theory of Hardy that an
increase of work would be required to move the particles of a liquid
among charged particles, so that if the "drops'5 were charged
an increase in viscosity might result. But by experiment Fried-
lander found that an electrical field was without noticeable
effect upon aa opalescent liquid.
Friedlander's values are expressed in relative units. Scarpa
(19O3) and (1904) has measured the viscosity of solutions of
phenol and water, expressing his results in absolute units. For a J jj
given temperature, he plotted the viscosities against the varying
concentration?, and obtained a point of inflection in the curves
at the critical-solution temperature. He tried to explain the
irregularities on the assumption that hydrates are formed. He
was apparently unfamiliar with the work of Friedlander.
Rothmund (1908) started from Friedlander's work to make a
study of the opalescence at the critical temperature. He meas-
ured the times of flow of butyric and isobutyric acid solutions in
water, noting particularly the effect upon the opalescence of U
adding various substances, both electrolytes and non-electrolytes.
He objected to the hypothesis of Friedlander in that, according
to the well-known formula of Lord Kelvin, small drops are less
stable than large ones, so that the former must tend to disappear.
Furthermore he remarked upon the entirely analogous opales-
cence which is observed in a single pure substance at its ordinary