168 Proceedings of the Royal Society of Edinburgh. [Sess. 
Table III. — Mass of Charcoal = T000 gm. 
1 
p. 
a. 
P- 
a. 
0T0 
21-4 
0-14 
26-9 
0-36 
54-2 
0’45 
6T0 
0-92 
87-6 
1-05 
95-1 
1-64 
123-5 
10-68 
266 
4-48 
193-8 
43-2 
358 
13-59 
283 
74-9 
443 
530 
370 
76*0 
475 
71 *7 
410 
74-6 
440 
75-4 
466 
In Table IV are found the calorimetric results. a is a mean value 
of a during the adsorption, and is usually calculated from a logarithmic 
interpolation formula. Save at the beginning, this value does not greatly 
differ from the arithmetic mean of the initial and final amounts adsorbed 
in any interval. Instead of expressing the heat of adsorption in calories 
per c.cm. adsorbed, the ratio XjXi is given of the isothermal heat of ad- 
sorption at constant volume to the “ internal ” heat of vaporisation of 
liquid sulphur dioxide. Thus with a usual notation 
V = (V 6 -V l )T^-P(V g -V l ). 
Again, since 
/?{Aj + P(V G — V L )} = A v Aa + G v . At . (Aa + Aa ), 
where G v is the specific heat at constant volume of the gas and Aa" is the 
gas entering the adsorption chamber and not adsorbed, we have 
^ = -£-(1-0934) -A t{ 1 + — V 001436). 
Xi Aa V Aa / 
To obtain X v in terms of calories per c.cm. absorbed, the ratio must be 
multiplied by 0'250. Estreicher from the vapour pressure measurements 
of Matthias and Chappuis calculated that the heat of vaporisation of 1 gm. 
sulphur dioxide at — 10° C. was 95’7 cal. Favre had found 88'2 cal. Estreicher 
as the mean of three very concordant measurements of volumes evolved on 
heating gives 95 • 9 cal. as the observed heat. Later, by weighing the gas 
after absorption by a liquid he gives 95’3 cal. at —11° C. The author 
from Regnault’s vapour pressure figures calculated 95'5 cal. at — 10° C., 
assuming with Estreicher the density of the dioxide to be normal, and using 
the equation 
\ = RT 2 ? lo fi P . 
dT 
