BETWEEN THE VISCOSITY OF LIQUIDS AND THEIH CHEMICAL NATURE. 549 
physicist. Their results serve to confirm the idea that the fatty acids, the fatty 
alcohols, and water, are liquids which contain congeries of gaseous molecules, and 
that acetone, glycol, propionitrile, and nitroethane belong to the same category. 
Thirty-six other liquids examined by them give, on the other hand, little evidence of 
association of molecules. Although this method of estimating molecular complexity 
has not been established by rigorous theoretical considerations either by Eotvos, or by 
Ramsay and Shields, it must be granted that there is now strong experimental 
support to the contention that liquids may differ from one another in regard to the 
complexity of their molecules. 
Since surface energy resembles viscosity, inasmuch as both are the result of extra- 
molecular effects, it is almost certain that the one as well as the other will be affected 
by molecular complexity. 
Hence, in dealing with viscosity, we must be prepared to find its magnitude 
influenced not only by the nature, number, and arrangement of the atoms composing 
gaseous molecules—intra-molecular factors which alone seem to operate in the case of 
properties like specific molecular volume and molecular refraction—but also by the 
extent to which the gaseous molecules become associated into complex groups in 
passing from gas to liquid. 
Graphical Representation of Results. 
After the observations of viscosity had been reduced, curves extending from 0° to 
the boiling-points of the particular liquids were plotted against viscosity coefficients as 
ordinates and temperatures as abscissae. On the scale adopted, 1 millim. corresponded 
to 0°'2 in temperature, and to ’00002 in the viscosity coefficient. On this scale a 
continuous curve could be drawn through the experimental points with little difficulty, 
as the observations taken in different limbs at the same temperature wmre often 
coincident, and were never so far apart as to admit of the introduction of any 
appreciable error by an arbitrary method of smoothing. 
On plotting the curves for a group of related substances on the same sheet of paper, 
marked regularities were often apparent between the relative disposition of the curves 
for the different members and their chemical nature. These regularities will lie 
apparent from the reduced representations of the curves given in the following pages. 
To avoid complication, the experimental points through which the curves are drawn 
have not been indicated ; it has to be remembered, however, that each curve represents 
on the average some 24 observations of the viscosity coefficient. The ordinates are 
multiplied by 10®. We now proceed to indicate the general features of these curves. 
Paraffins. 
The paraffins investigated were isopentane, pentane, isohexane, hexane, isoheptane, 
heptane, and octane. Fig. 5 represents the results obtained. In the case of the 
