132 
Transactions of the Boyal Society of South Africa. 
1^ 
Table VI. 
Modified Equation. 
A. 
B. 
L 
VkVk 
0-496 
14-75 
6-61 
21-36 
0-549 
13-92 
6-84 
20-76 
0-598 
13-16 
6-92 
20-08 
0-643 
12-44 
6-90 
19-34 
0-685 
11-75 
6-86 
18-61 
0-725 
11-07 
6-73 
17-80 
0-762 
10-37 
6-53 
16-90 
0-797 
9-66 
6-28 
15-94 
0-830 
8-91 
5-94 
14-85 
0-861 
8-10 
5-54 
13-64 
0-892 
7-22 
5-05 
12-27 
0-920 
6-24 
445 
10-69 
0-948 
5-08 
3-69 
8-77 
0-975 
3-59 
2-64 
6-23 
1-000 
0-00 
0-00 
0-00 
§ 6. On the Specific Heat of Saturated Vapours. 
In one of the papers to which reference has ah^eady been made (§ 1) 
the present writer used van der Waals's equation to investigate the 
behaviour of the specific heat of saturated vapours as a function of the 
limiting value of the ratio of their specific heats. As data were then (and 
still are) lacking by means of which the conclusions reached could be 
tested directly, an endeavour was made to obtain an experimental curve 
from the isopentane isothermals under a certain assumption regarding the 
behaviour of the specific heat at constant volume. That assumption has 
been criticized as being not in accordance with the law of corresponding 
states, and it has, therefore, been abandoned in the following treatment 
of the problem. Specific heats are first obtained by means of the modified 
equation (which has been shown to approximate more closely to ex- 
periment than the van dee Waals equation), and an experimental 
curve is then obtained from the isopentane isothermals, using the 
Kamerlingh Onnes equation of state for determining the change of 
C„ with volume. 
* H. Kamerlingh Onnes and W. H. Keeso.^i : Die Zustandsgieichung, Encyc. Math, 
Wiss., V. 10, 937 (1912) or Comm. Leiden. Suppl. No. 23, p. 323. 
