On an Experimental Modification of van der Waals's Equation. 131 
If VAN DER Waals's equation is used for the calculation in con- 
junction with the thermodynamical relation — 
we find- 
L 8 , 3^2 — 1 
while the moditied equation gives — 
L _ 
-1 
,+3. 
(19) 
(20) 
(21) 
When numerical values are obtained for (20), by means of the saturation 
constants of equation (1), we get, as the following table shows, reduced 
latent heats which are exactly one-third of the isopentane values at 
the same temperature. The same holds for carbon dioxide, for the latent 
heat curves for CO2 " and for isopentane practically coincide when 
reduced. 
L 
Pk'^k 
Table V. 
: VAN DER WaALS. 
L 
PkVk 
3. 
L 
PkVk 
L 
PkVk 
0-30 
8-91 
0-55 
8-40 
0-80 
6-48 
0-35 
8-87 
0-60 
8-17 
0-85 
5-76 
040 
8-80 
065 
7-88 
0-90 
4-82 
0-45 
8-71 
0-70 
7-51 
0-95 
3-50 
0-50 
8-58 
0-75 
7-05 
1-00 
When the latent heat is calculated from (21) instead of (20), the 
greatar part of this large discrepancy between actual and calculated 
values disappears. In the table, column A gives values of the first 
term of (21) and B gives values of the second term, each being obtained 
from the saturation constants of Table II. 
* KuENEN and Kobson : loc. cit. 
