BETWEEN THE VISCOSITY OP LIQUIDS AND THEIR CHEMICAL NATURE. 637 
Isomers. 
Normal and Iso Compounds. 
Normal. 
Difference. 
Iso. 
r,cP. 
Pentanes. 
687 
24 
663 
Hexanes. 
818 
19 
799 
Heptanes. 
931 
23 
908 
Propyl iodides. 
903 
25 
878 
Pi’opyl bromides. 
774 
24 
750 
Propyl chlorides. 
658 
14 
644 
Butyric acids. 
842 
- 1 
843 
With tlie exception of the butyric acids, which of those given above are probably 
the only liquids containing molecular aggregates, the normal compound has distinctly 
the higher molecular viscosity. In the case of the halogen compounds, the differences 
diminish with the fall in molecular weight; in the paraffins, however, there is no 
regularity in the variation of the differences. 
It may thus be assumed, as a first approximation, that the average effect of the 
iso mode of grouping is constant and operates so as to diminish the molecular 
viscosity by about 21 units. 
Aromatic Hydrocarbons. 
yfP. 
Difference. 
Ortho-xylene. 
954 
-15 
Ethyl benzene. 
939 
0 
Meta-xylene. 
939 
-16 
Para-xylene. 
923 
Of the four isomeric hydrocarbons, ortho-xylene has the largest, and para-xylene 
the lowest molecular viscosity. Ethyl benzene and meta-xylene give identical 
numbers, which are almost the mean of those of ortho- and para-xylene. 
