154 FLUIDITY AND PLASTICITY

where A and o> are constants and v is the specific volurP- ^
per gram. We have then

77 = BT

V — co

or

A+BT(v-u) '
It is truly remarkable that so simple an equation
can be employed with success to reproduce so complex
that for the fluidity isothermals of carbon dioxide passing
the critical state. To what extent it does do this is
Table XXXIX. Since the calculated values are nearly
small, it is evident that a better concordance could
secured by a happier choice of constants, but consider* ^S
difficulties in these measurements, the percentage of
between the calculated and the observed values is not
Having established a fairly exact relationship between-
and volume, and indirectly with temperature and
the problem of associated substances again presses
the foreground as it tends to do so often. A means
found for bringing these substances into conformity
others, but the solution is not yet forthcoming.
Dr. Kendall inquires in regard to the foregoing: —
formula of Batschinski of such great importance as
treatment of it would lead the readers to believe? IB it;
merely an interpolation formula? Would it not be
mention something about the alternative formula
(1918). The expotential formula of Arrhenius (1918) dLoos
lead us to a definite mental picture, and like many gtxxot
frankly empirical formula was omitted in this brief troa/tono.
of the subject. The relation of Batschinski fills a need ^wi
was felt in many minds, cf. p. 142. It leads us at oneo t
definite mental picture which is neccessary in building *ut]
consistent theory, so that we are now able to explain the rola/t
of fluidity to volume, temperature and pressure et ce£. i:
manner which is so natural, so unexpectedly simple and so ~fc>€
tifully in accord with observed facts that it is hard to soo "W
more evidence is needed to carry conviction.