( 611 ) 
that the method of the diameter gives the smaller value for tie 
critical volume. It was the deviation between the results obtained 
by these two methods that led Kamertincu Onnes and Kerrsom to 
undertake the study of the disturbance function which must ascribe 
a mutual relationship to these and similar deviations. Until it shall 
appear that this is not the case with argon and it shall be 
found that the two values agree, as is not impossible for this 
substance, we must assume that the above value (d, = 0.509) is 
smaller than that which would be given by an application of the 
diameter law to observations in the neighbourhood of the critical 
temperature, and this latter value is just the one that we require 
for our present calculations. In the meantime, however, there is no 
other course open to us than to base our calculations upon the value 
just given, 
Pa, so 
In this treatment of the question we neglect a difference which, 
if it could be considered equal to the differences usually existing 
between values of critical density as determined by these two methods 
would be much greater than that between the newly derived value 
and that used in Comm. 115 (dj = 0.496). 
As was mentioned in the beginning of this section a small change 
in the value of dj is sufficient to cause a large alteration of vapour 
volume, and it is accordingly remarkable that a good agreement is 
obtained between the observed values and those calculated with the 
value of dj, now deduced. We must ascribe this to the fact that a 
value of dj happens to have been found which is very suitable for 
the representation of coexisting liquid and vapour densities by the 
diameter, and this further leads us to suspect that the two methods 
of determining the critical density of argon will give results that 
differ but slightly from each other. 
The caleulations were made as follows: the diameter was drawn 
from the observations of Bary and Donnan in the neighbourhood of 
the boiling point of argon using the above value of dr, and the 
critical temperature lately published, — 122°.44 C. From the graph 
were read values of '/, (d, + d,) and from these and the observed 
values of d, —d,, d, and d, were calculated. The results are given 
in the following table. For the sake of completeness there are also 
inserted in the table densities d4, and d4, in terms of the normal 
density (the wt. of 1 1. of argon — 1.782 g. under normal conditions 
le) 
according to Ramsay and Travers *)) and volumes vy, and va, in 
1) W. Ramsay and M. W. Travers, Proc, R. S. 67. 329. 1900, 
