34

FLUIDITY AND PLASTICITY

experimental conditions. He used plain and silvered oscillating
glass vessels and a hollow metal sphere. Table XII proves
conclusively that slipping was absent in the former case.

Using the hollow metal sphere filled with water, LadenburfJ
obtained values of the viscosity which agree with the values found
by other methods, and shown in Table XIII.

TABLE XIII.—A COMPABISON or THE VISCOSITY OF WATER AS OBTAINED
BY DIFFERENT METHODS (LADENBTOG)

Method
n at 17.5°
17 at 19.2°
Observer

Efflux glass ...........
0.01076
0.01031
Poiseuille (1846)

Efflux glass ..............
0.01065
0.01027
Sprung (1876)

Efflux glass
0 01075
0.01030
Slotte (1883)

Efflux glass
0 01067
0.01025
Thorpe and Rodger (1804'

Oscillating solid sphere .....
0.01099
0.01054
W. Konig (1887)

Oscillating hollow cylinder. . Oscillating hollow sphere . . .
0.01082 0.01065
0.01037 0.01032
Miitzel (1891) Ladenburg (1908)

Ladenburg indicates how Helmholtz erroneously obtaim»c
his large coefficient of slipping by overlooking a point in th<
theory, and recalculating Piotrowski's data he finds that insteac
of the viscosity being 40 per cent greater than the general^
accepted value, this difference becomes only 3 per cent and^ thi
slipping becomes negligible.
It was stated above that the verification of the Law ol
Diameters of Poiseuille is a proof that slipping does not oceui
between glass and water. Knibbs (1895) has collected an
extensive table of observations of the viscosity of water at 10*
for tubes of various materials having radii varying from 0.0140 tc
0.6350 cm or nearly a thousand-fold, but there is no evidence oj
progressive deviation as the radius increases.
In experimenting on the possible effect of an electrical 01
magnetic field upon viscosity, W. Konig (1885) obtained zi
negative result. Duff (1896) seemed to detect an increase in the
viscosity of castor oil of 0.5 per cent using the falling dro|:
method and a potential gradient of 27,000 volts per centimeter
but for the most part the results were negative. Quincke (1897^