144

FLUIDITY AND PLASTICITY

If we could always compare the fluidities of liquids at a defini
multiple of the molecular limiting volume, it is evident that t.
effect of the volume, and therefore of temperature and pressu
in so far as they affect the volume, would be eliminated. Such
procedure would enormously simplify fluidity relationship
As a matter of fact Batschinski has shown that the molecul
limiting volume possesses an additive character, the values

I.IG

too.

"50 Fluidity 550
FIG. 55.—Relative volume-fluidity curves after Batschinski using the data c
Thorpe and Rodger.
4, Bromine; 5, nitrogen peroxide; 9, isohexane; 11, isoheptane; 13, trimethy.
ethylene; 14, isoprene; 15, diallyl; 16, propylchloride; 17, isopropylchloridc
18, isobutylchloride; 19, allylehloride; 20, methylenechloride; 21, ethylenechlc
ride; 22, ethylidenechloride; 23, chloroform; 25, perchlorethylene; 68, ethyl
benzene; 69, orthoxylene; 70, metaxylene; 71, paraxylene.
the atomic constants being H = 4.3, 0 = 8.6, C = 8.8, Cl =
19.2, Br = 24.8, I = 32.0, S = 19.0, a double bond = 3.3
and an iso-grouping = 0.7. For 53 of the substances studied b]
Thorpe and Rodger the differences between the observed anc
calculated values of the molecular limiting volume do not exceec
2 per cent. The limiting specific volume is approximately 0.301
. of the critical volume which is close to the parameter 6 of var
der Waals7 equation.
We are now in a position to get a very clear understanding
of the law that the fluidity is proportional to the free volume.