32 ■ Proceedings of the Royal Society of Edinburgh. [Sess. 
but allowed the adsorption to proceed with a fall in pressure and a decrease 
in volume of the system, we cannot apply any of the formulae (16), (17),, 
(18). The observed value will presumably fall between the values for 
the heat of adsorption at constant volume and the heat of adsorption at 
constant pressure. It will be noted that approximately 
'tp, T = 'h, T + RT, 
and hence it will be assumed that Titoff measured 
We have 
A, 
y, T 
T "" 2 R I — ^»,T+ JRT- 
- ( + RT approx. 
da 
g, T 
Hence if A were constant 
1 d A 
A da 
\>, T — "V • T 
dp 
0T 
(19) 
which corresponds to the Clapeyron equation. 
'dlogp 
In the tables below, RT 2 
0T 
22400 is given as calculated by the 
author from Ti toffs observations. Brackets round a value indicate that 
it is doubtful. From these values is calculated the heat of adsorption at 
0° C., and compared with the observed beat at the same temperature, a is 
measured in c.cm. gas per grm. at N.T.P., A in calories per c.cm. adsorbed. 
Table I. — Ammonia. 
p T 2 9 l°g P / 22400. 
0T / 
A. 
logio a - 
116° C. 
55°. 
15°. 
- 12°. 
0° calc. 
A calc. 
A obs. 
a obs. - a calc. 
2T0 
•298 
(•277) 
(•265) 
•386 
(■121) 
2-00 
'284 
•315 
•302 
•290 
•355 
•065 
1'80 
•306 
•351 
•331 
•319 
•360 
•041 
1-60 
•328 
•306 
•369 
•341 
•329 
•370 
•041 
1-40 
•328 
•323 
•375 
•352 
•340 
•375 
■035 
1-20 
•328 
•323 
•375 
•352 
•340 
•388 
•048 
l'OO 
•30 
•328 
(•38) 
. . . 
(•41) 
(•40) 
•41 
(•01) 
0-80 
•31 
•373 
*43 
0'50 
•41 
(•44) 
•45 
o-oo 
•42 
... 
The variation from pV = RT would not affect any of the calculated values more than 
1‘3 per cent., i.e. '005. 
