ON THE THERMAL PROPERTIES OF ALCOHOL. 
155 
T. 
P. (Reg.) 
P. (R. and Y.) 
O 
0 
12-70 
12-24 
5 
17-62 
17-15 
10 
24-23 
23-50 
15 
32-98 
3210 
20 
44-46 
43 95 
25 
59-37 
59-50 
30 
78-52 
78-05 
46. It will be seen from these results that our pressures are uniformly lower than 
those given by Regnault, except at 25°, where there is manifestly a misprint in his 
figures. The difference in pressure is approximately constant, and is equal to 0'46 mm. 
cly) 
The value of is considerably changed by this alteration, and the numbers given, 
except where the contrary is stated, have been derived from the formula, the 
constants of which were calculated by us for vapour-pressures. 
The Critical Point of Alcohol. 
47. In the ‘Philosophical Transactions’ for 1869, p. 583, Andrews gives a diagram 
showing, to some extent, relations between the pressure and volume of carbon dioxide 
at temperatures near its critical point. From our observations on alcohol we are 
enabled to give similar diagrams on Plate 6, showing the volumes of 1 gramme. 
The first of these (fig. 1) comprises observations between 90° and 243T°. The scale 
is necessarily a small one. The isothermal for 243T° has been mapped, and it is to be 
noticed that all other isothermals between these limits of temperature would fall 
between that line and the one representing volumes of saturated vapour. The 
numbers deduced from observations are represented by circles. Fig. 2 shows 
similar relations at temperatures between 220° and 246° on an enlarged scale, and it 
also exhibits the compressibility of the liquid. The highest temperature at which it 
was possible to measure both liquid and gas was 242'25° ; above that temperature 
measurement of gas was uncertain, owing to the slow rate at which condensation or 
evaporation proceeded. A successful measurement of the volume of the liquid was 
made at 242'6°, but it was still possible to distinguish liquid from gas at 243'0°; at 
243'1° the meniscus appeared to broaden and became indistinct. It disappeared abso¬ 
lutely on the least decrease of volume, owing to heat developed by compression, and 
it reappeared on increasing volume. The apparent critical point was therefore at this 
temperature, but the pressure remained perfectly constant during considerable change 
of volume. A similar phenomenon has been noticed by Ansdell, and we agree with 
him that the real critical point must lie somewhat higher. In the diagram on 
Plate 6 a dotted line has been drawn connecting the curves showing the volumes of 
x 2 
