142 FLUIDITY AND PLASTICITY
in another direction, for generally speaking whenever T ^
are mixed and a contraction takes place, there seemt- " '
decrease in fluidity. Alcohol and water, acetic acid '' '
and chloroform and ether are a few examples. On th* 4
when liquids mix with an expansion in volume, the mi%
greater fluidity than we would expect from the linear ftf *
ume concentration curve. Methyl iodide and carbon ' 4 j
furnish an example of this sort (BinghameZ al.91913). *
facts have suggested to various workers (Brillouin (I * **
2, p. 127; Dunstan and Thole (1909), p. 204; Bingh?*f
p. 270) that fluidity and volume are intimately relate *
in fact than fluidity is to either temperature or presmi* *
In spite of this intimate relationship, it has been lit f *v
gated. Slotte (1894) stated that the logarithms of th< 1
are proportional to the logarithms of the specific veil**
from this observation he deduced his second Eq. (48).
most important discovery was made by Batschinski in I r 4
found that the relation between the molecular volume *
fluidity may be expressed in the following formula:
0 = 0(7- Q)
where 0 and C are constants. The constant 0 may be* * ipl
the limiting value which the molecular volume of any iir j
have as its fluidity approaches zero, and it is theref'**'
the "molecular limiting volume.7' Consequently the *i«
V — Q may be called the " molecular free volume5" and ft*
relation may be very simply expressed as follows: Th*~
varies directly as the free molecular volume. Sixty-six n * <
substances investigated by Thorpe and Rodger exhibit f I
tionship and the* values of the fluidity, as calculated f r
volume, seldom deviate from the observed values by m*-*
1 per cent. The 21 substances for which the agreeni**iu1
good include the alcohols, water, some of the acids, the fit t«
drides, and some of the halides. These substances arc*
regarded as associated and it may well be that the u**,
weight is not constant as the temperature is raised. Tit**
of the very remarkable agreement obtained is shown t*i
XXXVII containing data for benzene obtained by Thf*r
Rodger between 0° and the boiling-point and by Hey«l