ON THE THERMAL PROPERTIES OP ALCOHOL. 
141 
29. It will be seen from these numbers that the values of L increase regularly to 180° 
with fall of temperature. They then appear to remain approximately constant. It is 
at this temperature also that the vapour-densities become uncertain, and show a 
tendency to rise. From the nature of the equation used to obtain the values of L 
any discrepancy in the vapour-densities will affect the values of L. At temperatures 
below 180°, as explained in § 23, the error introduced becomes considerable, and the 
experimental results are evidently no longer trustworthy. But above this temperature 
the ratios of the specific gravity of the liquid to that of the gas becomes sufficiently 
small to give accurate results ; and the accuracy is confirmed by the regularity of the 
deduced curve. 
30. There are already data as regards the heat of vaporisation of alcohol. Andrews 
(Chem. Soc. Journ., I., p. 27) gives the value of L for 77'9°, under a pressure of 760 nuns., 
as 202-4 cal. Favre and Silbermann ( l Annales’ (3), 37, p. 465) give at the boiling- 
point under normal pressure 208*92 cal. PvEGNAULT (‘Memoires de l’lnstitut,’ xxvi., 
pp. 819 and 262) gives a number of values of the total heats, from which the heats of 
vaporisation may be calculated by subtracting the specific heats of the liquid, calcu¬ 
lated according to the formula given by him :— 
logSp. Ht. = 1-7384166+3-0499296^ + 6-3436027^. 
These numbers are as follows, and we append the volumes of saturated vapour and 
the resulting vapour-densities calculated from his numbers. They are shown graphi¬ 
cally on the accompanying curve in Plate 4 (1) :— 
T. 
Total heat. 
Latent heat. 
dp 
dt 
Yol. of 1 gram, of 
vapour. 
Yap. density. 
O 
0 
eentims. 
236-5 
236-5 
0-854 
33,435 
21-08 
10 
24L4 
238-8 
1-525 
17,297 
21-00 
20 
252-0 
240-6 
2-565 
10.008 
20-48 
30 
258-0 
240-5 
4-23 
5,866'8 
20-45 
40 
262-0 
238-2 
6-82 
3,489 
20-865 
50 
264-0 
233-5 
10-635 
2,126 
21-50 
60 
265-0 
227-6 
15-975 
1,338 
22-11 
70 
265-2 
220-6 
23-14 
877-5 
22-26 
80 
265-2 
213-1 
32-43 
583-0 
23-16 
90 
266-0 
206-0 
44-19 
402-6 
23-57 
100 
267-3 
199-1 
58-73 
285-4 
23-94 
110 
269-6 
192-9 
75-60 
209-5 
24-01 
120 
272-5 
186-8 
97-0 
154-5 
24-47 
130 
276-0 
181-0 
123-35 
119-7 
24-22 
140 
280-5 
175-8 
152-05 
89-02 
25-42 
150 
285-3 
170-5 
186-5 
69-11 
26-01 
As alcohol cannot without dissociating possess a vapour-density less than 23, the 
numbers below 80° are manifestly wrong. 
Andrews’ measurement gives a vapour-density of 23*51 ; and Fayre and Silber- 
