60

FLUIDITY AND PLASTICITY
TABLE XXL—VISCOSITY OP AIR AT 15°

Method
9
Observer

Transpiration ...............
5,507
Breitenbach (1899)

Transpiration ............... .
5,502
Schultze (1901)

Transpiration
5 528
Markowski (1904)

Transpiration
5,502
Schrnitt (1909)

Transpiration
5.531
Knudsen (1909)

ing data might be improved by a critical study for the purpose
of making the needed corrections. It is a curious fact that the
kinetic energy correction has been so little understood and appre-
ciated. Even in the case of liquids it is very commonly neglected
although it may amount to several per cent of the viscosity to
be measured. It is sometimes stated that no kinetic energy
correction is necessary when liquids now through a capillary from
one reservoir to another and not into the air. The Ostwald
viscorneter (cf. p. 75), is used more than any other but it appears
that no kinetic energy correction is ever applied. It is true that
the instrument is used for relative measurements only, but this
fact does not cause this correction to be without effect in the cal-
culation, for the reason that the kinetic energy correction is not
proportional to the viscosity.
There may be those who would maintain that the correction
for kinetic energy, as given above, is not the correct one to apply
to gases, cf. Fisher (1909). But that a correction is unnecessary
cannot be maintained even in the case of gases, in view of Hoff-
mann's work on the interrupted now of gases. One of Ms capil-
laries was cut into 28 pieces without loss. In flowing through the
interrupted capillary, the kinetic energy correction would be
increased twenty-eight fold, as has been already indicated on page
28. As a matter of fact the time of flow was considerably
greater in the interrupted capillary, proving the importance of the
correction. It would be particularly interesting to see whether
an experimental verification of the correction would be obtained
by an intensive study of the data of Hoffmann (1884).
The term "specific viscosity" has been very largely used and
may here receive brief comment. Water at 0° has been taken
as a standard with a specific viscosity of 100, but water at 25°