660 
PROFESSOR W. RAMSAY AND DR. J. SHIELDS ON THE 
This equation seems to signify that the molecules are in a condition of equilibrium, 
inasmuch as it would imply that and the surface-tensions of the liquids, 
balance the pressures on the surfaces of the liquids ; but as a vertical pressure cannot 
be balanced Ijy a horizontal stress, perhaps it is right to assume that only proportion¬ 
ality is meant. 
Equation (2), by appropriate multiplication, becomes 
Now from (1) 
hence 
(3) Tdlb Iff . 
^ 2^2 *^2 
When two substances are in corresponding conditions they remain so, according to 
Van dee, Waals, when the temperatures change proportionally to and Tg, or, in 
otlier words, when the change of condition with temperature at any corresponding 
temperatures is proportional to the temperatures. Hence Eotvos argues that 
n^ ^ [W] _ A /V2’V\ 
1 dT V H / ^^ZTVE/’ 
This equation implies that the rate of change of temperature of the molecular 
surface-energy of any two liquids is the same. 
We have deemed it necessary to enter at some length into the views of Eotvos, 
because, although his conclusion is true for those liquids which we have investigated 
between wide ranges of temperature, his premises are scarcely justifiable. 
This is best tested numerically; and although Young has done so in numerous 
papers, it will be convenient to show the magnitude of the error for a specific case. 
It is easy to test equation (1) stated in the form ppq/T;^ = from data given 
by Ramsav and Young (‘Phil. Trans.,’ 1887, A, pp. SI and 85) for ether, and by 
Young (‘Trans. Chem. Soc.,’ 1889, pp. 501 and 504) for benzene. 
Benzene. 
Ether. 
Corresponding temperatures .... 
339‘95° Absolute 
28il-95° Absolute 
Pressures at these temperatures 
495’5 millims. 
291-1 millims. 
Molecular volumes at these temperatui’es 
03’95 cub. centims. 
101-86 cub. centims. 
pt' 
T 
136-94 
104-79 
These numbers, according to Eotvos, should be equal, i.e., 136'94 = 104'79. 
