588 
MESSRS. T. E. THORPE AHD J. W. RODGER OX THE RELATIONS 
unit distance equal to unity. It seemed, however, that relations betw-een viscosity 
and chemical nature would best be brought to light if instead of adopting merely unit 
areas we selected areas which were related to the specific molecular volumes of the 
liquids. If M be in grams a weight of substance numerically equal to its molecular 
weight, and if p be the density of the liquid. M/p is the specific molecular volume d^, 
or a volume of liquid in cub. centim. which contains for different substa,nces the .same 
number of gaseous molecules. 
# evidently gives in sq. centim. the area of the face of a cube which may be taken 
to represent the specific molecular volume. This area Tve term the specific molecular 
area and the product of rj and the specific molecular area (y) X cZ’) we term the 
molecular viscosity. With the units employed, it is the force in dynes which has to 
be exerted on a liquid surface equal to the specific molecular area in sq. centim. in 
order to maintain its velocity equal to unity under the unit conditions laid down in 
the definition of the viscosity coefficient. 
In the absence of a dynamical theory of the nature of liquid viscosity if we assume, 
as has already been done by Eotvos, that on the specific molecular area there are 
distributed, on the average, the same number of molecules, the molecular viscosity 
may be taken as proportional to the force which has to be exerted on a liquid 
molecule in order to maintain its velocity equal to unity under unit conditions. 
(3) Values of rj X Specific Molecular Volume. The Molecular Viscosity Work, 
(y X #.) 
The product of y and the specific molecular volume exhibits relations to chemical 
nature of the same kind as those given by molecular viscosity. This product yd^ is 
evidently the molecular viscosity multiplied by cl which is the length in centimeters 
of the edge of tlie cube which represents the specific molecular volume, and this 
length we term the specific molecular length. ycT has evidently the dimensions of 
work, and for this reason we term it the molecular viscosity work. In ordinary units 
it is the work in ergs required to move a liquid surface equal to the specific molecular 
area in sq. centim. through the specific molecular length in centim. under unit 
conditions. If the specific molecular length be assumed to be proportional to the 
average distance between the centres of two adjacent molecules the molecular 
viscosity work is proportional to the work spent in moving a molecule through the 
averao^e distance between two molecules under unit conditions. 
In deducing the specific molecular volumes, specific molecular areas, etc., gaseous 
molecular weights were employed. It was therefore to be expected that the relation¬ 
ships between the magnitudes of the molecular viscosity and molecular viscosity work, 
existing in the case of liquids for wliich the liquid and gaseous molecular weights 
were identical, would no longer be the same when the liquids contained aggregates 
of gaseous molecules. By this mode of treatment it w^as hoped that if these mag- 
