BETWEEN THE VISCOSITY OF LIQUIDS AND THEIR CHEMICAL NATURE. 667 
molecule. It is noteworthy that the difference between the values of the molecular 
viscosity work of diallyl and isoprene is 72, a number which is lower than the mean 
value for a difference in composition corresponding to CH 2 , viz., 80. If diallyl be 
represented as 
Oils : CH.CH3.CH0.CH : CHs, 
the above small difference may be taken to indicate that isoprene is not a true 
homologue of diallyl, and probably, therefore, that the formula for isoprene which most 
closely resembles the formula for diallyl, viz., 
CH3:CH.CH3.CH:CH2, 
is not the correct formula. The conclusions which follow from the viscosity of 
isoprene, taken in conjunction with the fact that isoprene yields acetic acid as an 
oxidation product, point to 
CHg.CH : C : CH.CHg 
or 
CHg.CH :CH.CH :CH3 
as the most probable formula for this hydrocarbon. 
Methyl Iodide. —The difference betweeji the theoretical and calculated values for 
methyl iodide is considerably above the average. 
This is no doubt due to the fact that methyl iodide is a substituted methane ; it is, 
indeed, the only monocarbon compound given in the table; in all the other iodides 
iodine has been introduced into a methyl group. (Compare what follows with regard 
to carbon tetrachloride, which is also a monocarbon compound.) 
Fatty Acids. —As has already been stated, the acids most probably contain 
molecular aggregates at the temperatures of comparison. The fairly regular values 
given by the normal acids for the effect of CH 3 and O indicate, however, that at 
temperatures of equal slope the extent of the molecular aggregation if not quite the 
same is not very different for the various liquids. 
Isobutyric acid has probably a slightly different molecular complexity at equal 
slope from that of the corresponding normal acid. The same result, indeed, follows 
from surface-energy observations. This is no doubt the reason why in all comparisons 
nto which this iso acid enters it gives values which appear more or less anomalous 
when compared with those given by non-associated licjuids or by liquids like the 
normal acids, which are probably of about the same degree of association at equal 
slope. 
Isomeric Aromatic Ilydrocarhons. —The calculated value is the same for all the 
compounds, and is deduced from the values of carbon, hydrogen, and the effect of the 
ring-grouping. 
Ethyl benzene and meta-xylene give observed values which are identical with those 
calculated, whereas ortho-xylene gives a number which is as far above the calculated 
4 Q 2 
