638 MESSRS. T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
Dichlorethanes. 
>jd^ 
Difference. 
Ethylene chloride. 
737 
- 35 
Ethylidene chloride. 
702 
The symmetrical compound has here decidedly the larger value. 
Isomeric Ketones. 
tjd^. 
Difference. 
Diethyl ketone. 
Alethyl-propyl ketone .... 
785 
796 
11 
Here the unsymmetrical compound, probably for the reason already given, has the 
larger molecular viscosity. 
Quantitative relations fairly definite in character are thus exhibited in the preceding 
tables between the magnitudes of the molecular viscosities. 
The tables of homologous and corresponding compounds show that molecular weight 
exerts an approximately regular effect, and the comparisons of normal and iso com¬ 
pounds, and of propyl and allyl compounds, indicate that the effect of constitution can 
also in some cases be quantitatively estimated. 
We have, therefore, attempted to ascertain if molecular viscosity can be expressed 
as the sum of partial effects which may be ascribed to the atoms and to the modes of 
atom linkage which occur in the molecule. The details of the method of calculation, 
which is the same as that employed in the case of the comparisons at the boiling- 
point, are given in what follows. 
Method oi Deducing the Fundamental Viscosity Constants (Molecular 
Viscosity at Slope -04^323). 
Value q/’CHg. 
From the table of homologues the mean of the twenty-three values for the effect of 
CHg is 120. Neglecting signs, the average difference from the mean is 12. It is 
therefore assumed that 
CHg = 120. 
