CHAPTER IV

IS THE VISCOSITY A DEFINITE PHYSICAL QUANTITY?

So long as the theory was so imperfectly worked out that
the values for the viscosity of a well-defined substance like
water were different when obtained with different forms of
instruments, it was inevitable that the whole theory and practice
of viscosity measurement should have been called into question.
Among numerous researches, we may cite in this connection
those of Traube (1886), Wetzstein (1899) for liquids,- Fisher
(1909) for gases, and Reiger (1906) for solids. Since the limita-
tions and corrections discussed in the preceding chapter have
evolved very gradually, many of these researches are now of
historical interest only, and their discussion here would be as
tedious as it is unnecessary. Enough material has already been
given to prove that viscosity is an entirely definite property for
liquids. Table IX proved that tubes of quite diverse dimen-
sions give entirely harmonious results. This has been confirmed
repeatedly, especially by Jacobson, 1860, working with tubes of
considerably larger bore. Not only are the results obtained
with the transpiration method in agreement, among themselves,
they also agree with the results from various other methods, as
shown in Table XIII.

Knibbs (1896) has made a critical study of the existing data
for water, recalculating and using the corrections suggested
in the last chapter. The result was not satisfactory. Many of
the measurements were found to be uncertain and as a result of his
study Knibbs doubted whether it was yet possible to determine
the viscosity of a substance like water with an error of much less
than 1 per cent from 0 to 50°, or 5 per cent from 50 to 100°.
During the last 20 years investigations have been carried out,
which give thoroughly satisfactory and concordant results, as is
shown by Table II in Appendix D. The improvement is due
to a happier disposition of apparatus for controlling the different
correction factors.

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