ON EVAPORATION AND DISSOCIATION. 
113 
acetic acid may exhibit this behaviour, yet that its abnormal density is to be explained 
chiefly on Playfair and Wanklyn’s supposition. Horstmann and others take the 
opposite view. So far, then, it is an open question whether acetic acid dissociates or 
not. 
§ 71. Numerous determinations of the vapour-pressures of acetic acid have been made 
by Regnault (‘ Memoires de 1’ Academic’, xxvi., p. 51-60), Bineau (‘Annales’ [3], 18, 
p.226), Landolt (‘ Annalen,’ Suppl., 6,p. 157), and Wullner (Pogg. Ann., 103, p. 529). 
Their results show absolutely no concordance. Thus at 15°, Bineau finds a vapour- 
pressure of 7 millims.; while Landolt finds 15 millims.; and Regnault’s determina¬ 
tions vary from 8 '5 millims. to 10 ’4 millims. At higher temperatures the various 
determinations are even less concordant. At 80°, for example, the difference between 
determinations by Landolt and by Wullner amounts to 85 millims. Pegnault 
attributed his discordant results to the presence of water in those samples which gave 
a lower pressure, and of acetone in those giving a higher pressure. It will be seen that 
our very numerous determinations exhibit perfect accordance with each other. The 
vapour-pressures and the temperatures of volatilization at low temperatures have 
already been given by us in the paper referred to; above 20° the results are as 
follows :— 
§ 72. Vapour-pressures of Acetic Acid in Barometer-tube. 
Series I. 
Temperature. 
Pressure. 
Temperature. 
Pressure. 
Temperature. 
Pressure. 
O 
millims. 
O 
miliims. 
O 
millims. 
21-2 
127 
39-2 
32-2 
63-2 
100-7 
24-5 
14-6 
43-8 
39-7 
66-0 
113-4 
29-15 
18-55 
48-1 
49-9 
68-7 
127-7 
31-0 
20-45 
51-5 
58-7 
711 
142-5 
33-2 
23-2 
54-9 
68-3 
73-4 
157-0 
34-4 
24-25 
57-6 
77-4 
75-5 
1701 
35 6 
26-45 
60-2 
88-5 
78-1 
190-7 
Series II. 
Temperature. 
Pressure. 
Temperature. 
Pressure. 
Temperature. 
Pressure. 
O 
millims. 
O 
millims. 
O 
millims. 
25-9 
15-05 
45-1 
42-65 
66-15 
114-6 
28-3 
177 
49-6 
52-9 
68-15 
126-0 
30-95 
20-25 
53-2 
63-6 
70-05 
136-1 
34-3 
25-25 
57-0 
75-5 
72-95 
153-6 
37-4 
29-2 
59-9 
86-5 
74-6 
164-5 
40-8 
34-5 
63-2 
101-2 
77-95 
188-1 
After the completion of these experiments it was found, on inclining the tube, that 
absolutely no air was present. 
mdccclxxxvi. o 
