CHANGE FROM THE LIQUID TO THE SOLID STATE ON YAPOUR-PRESSURE. 467 
Series VIII. 
Temperature. 
Pres-lire. 
State. 
millims. 
25'60 
1595 
Liquid 
22-05 
13-05 
21-68 
12-85 
19-20 
11-05 
17-00 
9-75 
16-41 
9-45 
Solid 
16-32 
9-15 
16-20 
9-10 
16-09 
8-95 
15-80 
8"85 
156 
8-55 ■ 
14-9 
8-55 
Liquid 
14-85 
8-00 
Solid 
14-58 
7-95 
14-30 
7-20 
13-30 
6-75 
12-60 
6-65 
1210 
6-05 
9-16 
4-70 
6-41 
3-75 
2-86 
2-8 
” 
13. On inspection of the curves representing the above numbers (Plate 19), the 
truth of Professor Thomson’s theory is evident, for in the case of acetic acid, both 
the solid-gas curve and the liquid-gas curve have been obtained at temperatures 
below the melting-point. 
14. An attempt was next made to measure these differences by the barometric 
method. As it is important in such experiments to ensure complete absence of air, the 
methods of introducing the liquid into the barometer tube may here be noticed. In 
the first series, the following method was employed. The little apparatus a, Plate 18, 
%. l,was partly filled with acetic acid, and exhausted with the pump, so as to remove 
dissolved air. A straight barometer, boiled out as usual, was placed in position. 
The little apparatus was removed from the pump, the point was broken off under the 
mercury, in the trough in which the barometer-tube stood, and a l ittle of the acid forced 
up into the tube. There was a trace of air as large as a pin-point observable on 
slightly inclining the barometer-tube so as to bring the liquid to the top, which, 
however, was rapidly redissolved by the acetic acid. 
15. Various attempts were made to secure constant low temperatures, which could 
be rapidly varied at will. The apparatus shown in b, Plate 18, fig. 1, was found best to 
answer the purpose. The tube, serving as a jacket to the upper portion of the barometer- 
tube containing the acid, was half-filled with ether, through which a current of dry air, 
regulated by means of a stop-cock, was drawn by an injector. The temperature 
rapidly fell, and remained constant so long as the rate of the current of air was not 
altered. Hie uniformity of the temperature of the ether was ensured by the violent 
agitation caused by the bubbles of air. Fresh ether was admitted from time to time 
