SECTION III, 1912 [95] Trans. R. S. C. 
On a Thermodynamic Measure of the Degree of Polymerization of Liquid 
Substances. 
By M. M. GARVER. 
Presented by JAMES Loupon, LL.D. 
(Read May 16, 1912). 
At the present time physical chemists are dependent almost en- 
tirely upon two general sources for their knowledge of the molecular 
constitution of liquid substances; (a) the remarkable generalizations 
of van der Waals and the experimental results due to many investiga- 
tors embodied in the numerous tests of the van der Waals equation, 
and (b) the monumental experimental work of Sir W. Ramsay and J. 
Shields' in connection with their modification of the equation of Eôtvôs. 
These two sources of information, each interpreted in connection with 
the corresponding experimental data do not always lead to consistent 
results although both agree in attributing to special classes of liquids 
a considerable degree of polymerization. In the interest of pure science 
it is very desirable that a reliable criterion of the molecular changes 
accompanying the process of condensation from the vapour to the liquid 
phase should be established. The theoretical foundation of the method 
of Ramsay and Shields is not fundamental, and when accepted at all, 
is accepted as open to doubt. In the first place the latter method, 
based as it is on the surface tension of the liquid, is capable of giving 
only relative values as compared with certain substances taken as 
standards because they agree with each other in possessing the same 
surface-tension-temperature characteristics. But what proof is there 
that the half-dozen standard liquids are not polymerized? 
The van der Waals’ equation was originally based on the principle 
of continuity between the vapour and liquid states on the assumption 
that there is no material molecular change accompanying the transition 
from vapour to liquid and vice versa. Latterly, van der Waals has 
concluded? that all substances in the liquid phase must consist, more or 
less of polymerized molecules. This latter conclusion is at variance 
with the Ramsay and Shields’ criterion. The subject is then in a some- 
what unsettled state so that a reliable criterion containing only assump- 

1 Zeit. phys. Chem. 12 433 (1893). 
? Die Zustandsgleichung. See remark by Pro. Bancroft, Jour. Phys. Chem. 
15, 9. (1911), p. 822. 
