112 
PROFESSOR W. RAMSAY AND DR. S. YOUNG 
§ 68. Maximum Temperatures at Different Pressures. 
In these experiments the only differences from the ordinary arrangement were—a 
stopcock was used instead of an indiarubber tube and clip to admit the liquid ; as 
nitric peroxide attacks cotton-wool, the bulb of the thermometer was covered with 
asbestos ; warm water was used as a jacket, and the condenser was placed in a good 
freezing mixture. 
Pressure. 
Temperature. 
Pressure. 
Temperature. 
Pressure. 
Temperature. 
millims. 
O 
millims. 
O 
millims. 
O 
86-5 
-19-35 
257'5 
o-o 
483-0 
12-1 
91-8 
-18-15 
291-0 
+ 2-2 
536-0 
14-2 
] 13-5 
-14-60 
316-5 
4-0 
578-5 
15-8 
127-0 
-12-7 
344-0 
5'7 
613-5 
17-0 
147-5 
-io-o 
390-5 
7-9 
660-5 
18-5 
177-0 
- 6-7 
426-0 
9-7 
738-5 
20-9 
204-5 
- 4-3 
467-5 
11-4 
752-0 
21-5 
§ 69. On reference to the curves (Plate 1) it will be seen that the results by both 
methods agree as closely as could be expected from the nature of the first. In this 
respect the behaviour of nitrogen peroxide is similar to that of ammonium chloride ; 
but while the latter is completely dissociated at its volatilizing point under normal 
pressure, the former has suffered only very partial dissociation. 
Note.— Quite recently E. and L. Natanson (‘Wiedemann’s Annalen,’ 24, p. 454) 
have determined the relations between the specific heat and vapour-density of 
nitrogen peroxide under varying pressures, and at a constant temperature. They find 
that while the vapour-density increases, the specific heat decreases with rise of 
pressure, and conclude from this that the alteration of density of nitrogen peroxide is 
due to the dissociation of No0 4 into 2N0 3 . 
§ 70. Acetic Acid .—The sample of acetic acid used was the same as that em¬ 
ployed by us in determining the different vapour-pressures of the solid and liquid 
acid (see ‘ Transactions,’ 1884, Part II.). It was perfectly pure, boiling with absolute 
constancy at 118*7°, at a pressure of 765*2 millims., and melting at 16*4°. The large 
stock of acid contained a little water; but on fractionation, after one-third had 
distilled over, the remainder always boiled constantly to the last drop. The various 
determinations were made with portions fractionated at different times. 
Playfair and Wanklyn (Trans. Roy. Soc., Edin., 22, Part IIP, p. 441) were the 
first to suggest that, as the vapour-density of acetic acid at low temperatures is nearly 
double that which it possesses at high temperatures, its formula at low temperatures 
is C 4 H 8 0 4 ; and that on heating, this molecule splits into two of the formula C 3 H 4 0 3 . 
An increase of density in the neighbourhood of the condensing-point is a common pro¬ 
perty of all gases; and Naumann concludes (‘Annalen,’ 155, p. 325) that, although 
