FLUIDITY AND THE CHEMICAL COMPOSITION

119

This gives an average value for oxygen of 24.2 with an average
divergence of 1.3 from this mean. From these values, the
absolute temperatures corresponding to a fluidity of 200 may be
calculated. Some of these calculated values are given in the
fifth column of Table XXV. A comparison between these
calculated and the (observed values for 35 substances shows an
average percentage difference of less than 0.8 per cent.
Association.—In attempts to establish a relation between
viscosity and chemical composition it has been customary to
disregard entirely the fact that certain classes of substances are
known to be highly associated, and hence the molecular values as
calculated from the atomic constants cannot be expected to agree
with the observed values. A more logical method of procedure
would be to use known values of the association in arriving at
the calculated molecular temperatures. The difficulty of this
method is that the values of the association as given by different
methods do not agree very closely and even the methods of
getting these values have been subjected to criticism. It seems
best therefore to reverse the method and use our atomic constants
to calculate the association, which can then be compared with the
values of the association obtained from the surface tension,
volume, et cetera.
In the calculation of the atomic constants as given above,
it was assumed that the compounds chosen were non-associated.
This is not entirely warranted, but they must be associated to
approximately the same extent since the agreement between the
calculated and observed values is generally satisfactory, and it is
the general belief that some of these compounds are indeed
unassociated. It is highly probable that association or constitu-
tion is responsible, in part at least, for the uncertainty in the
so-called "constants," but this uncertainty can be removed by
further amplification of our data.
Since the atomic constants are additive, it follows directly
that the association will be given by the ratio of the observed to
the calculated values of the temperature corresponding to the
given fluidity. Thus for water (E^O)* at the fluidity of 200
the absolute temperature is 328.9, while the value calculated
from the gas formula H20 is 2 X 59.2 + 24.2 = 142.6. The
association factor (x) at the temperature of observation (328.9°