634 
MESSRS. T. E. THORPE AND J. W. RODGER ON THE RELATIONS 
the cases of the acids, the dibromides, and the anhydrides. In the case of the 
dibroinides an unsymmetrical compound is compared with a symmetrical compound, so 
that the value for CHg is probably affected by constitutive influences, and, as regards 
the anhydrides, the unsatisfactory character of the propionic anhydride may be the cause 
of the smallness of the difference. It is signiflcant that the differences given by 
homologous acids, although irregular, are not very far removed from those given by 
other series of homologues. 
Corresponding Compounds. 
Iodide. 
Bromide. 
Chloride. 
Acid. 
Alcohol. 
Diff. 
Tjd?. 
Diff. 
Diff. 
lydh 
Diff. 
tjdr. 
Methyl. 
638 
182 
456 
280 
358 
Ethyl. 
778 
115 
663 
185 
593 
Propyl. 
903 
129 
774 
116 
658 
161 
742 
Butyl. 
• • 
842 
Isopropyl .... 
878 
128 
750 
106 
644 
Isohutyl. 
1010 
133 
877 
117 
760 
167 
843 
Allyl. 
864 
130 
734 
117 
617 
Ethylene .... 
• • 
973 
(118) 
737 
Here it is seen that an iodide has on the average a molecular viscosity which is 
about 127 units larger than that of the corresponding bromide. 
A bromide gives a molecular viscosity which, on the average, is 115 units greater 
than that of the corresponding chloride, the average difference from this mean value 
being only some 3 units. An iodide has, on the average, a molecular viscosity which 
is 174 units greater than that of the corresponding acid. Methyl alcohol has a mole¬ 
cular viscosity which is also considerably lower than that of methyl iodide. It is, 
therefore, evident that the corresponding compound of higher molecular weight has 
the higher molecular viscosity, and where two series of corresponding compounds, the 
fatty acids included, can be compared, the differences obtained are approximately 
equal. 
