130 
Transactions of the liouat Society of South Africa. 
§ 5. Latent Heat. 
As a further test of the improvement effected by the foregoing 
modification, we may use the new constants for calculating values of 
the latent heat at different temperatures. The external work (reduced) of 
vaporization — 
Wfe.^, = 7r,((.,-(.,) ...... (17) 
is only a fraction of the total latent heat, and yet even there an improve- 
ment is already evident, quite marked with respect to dependence on 
temperature although the change effected in the absolute magnitude of the 
work is not so great. Van der Waals's equation gives 1-42 at ^ = 0-6, 
rising to a maximum of 1-47 at ^? = 0'7 and, of course, falhng to zero at the 
critical point ; while at ^ = 0 61 isopentane gives 2-22, rising to a maximum 
of 2"42 at ^ = 0-76. Values calculated from the saturation constants of 
Table II. give 1-57 at ^ = 0-60 rising to a maximum, 1-80, at ^ = 0-76. As 
before, carbon dioxide and isopentane correspond very well. 
The experimental values of the latent heat have been obtained from 
the well-known equation — - 
L = T^'K-t>,) (18) 
and the following table contains the values of the reduced latent heat, 
Li/pj^v,,, thus found for isopentane. 
Table IV. 
IsoiJentane. 
L 
PkVk 
L 
PkVk 
,3r. 
L 
PkVk 
0-614 
25-00 
0-788 
19-88 
0-961 
10-09 
0-686 
24-41 
[ 0-809 
19-07 
0-974 
8-60 
0-658 
23-72 
j 0-831 
18-19 
0-983 
7-257 
0-679 
2317 
0-853 
17-23 
0-990 
5-991 
0-701 
22-59 
i 0-875 
16-21 
0-994 
4-849 
0-723 
21-95 
i 0-896 
15-03 
0-996 
4-127 
0-744 
21-22 
1 0-918 
13-74 
0-998 
3-071 
0-766 
20-61 
1 0-940 
12-15 
0-999 
2-376 
J. p. KuENEN and W. G. Kobson : Phil. Mag. (6), 3, 155 (1902). 
