1916-17.] The Adsorption of Sulphur Dioxide by Charcoal. 169 
Correcting for the departure from the gas law, we get 932 cal. at — 10° C.* 
Taking 93'2 cal. as the heat of vaporisation of one gram of the dioxide at 
— 10°, the factor 0‘250 is easily calculated. 
Table IV. 
a. 
a. 
Kl\- 
8-0 
1-870 
9-9 
1-770 
339 
1-616 
40-7 
1-576 
68-9 
1-554 
75-7 
1-469 
103-5 
1-426 
120-4 
1-395 
137-8 
1-381 
177-5 
1-370 
176 
1-306 
291 
1-350 
210 
1-443 
337 
1-318 
242 
1-417 
374 
1-142 
270 
1-407 
402 
1-049 
303 
1-349 
409 
0-989 
338 
1-310 
361 
T257 
378 
1-075 
398 
1-026 
424 
0-993 
454 
1-012 
The results of Table III are presented in graphical form in fig. 3. The 
curve is of the same type as that obtained by Troutonf for the adsorption 
of water vapour by flannel. In the present case the upward bend occurs 
much later than p/P = *2, the inflexion occurring about p/P = '63 and the 
bend being pronounced only after pfP = *9. The gradient does not appear 
to be infinite near p/T= 1. 
The calorimetric observations are shown in fig. 4. It will be seen that 
a minimum heat of adsorption is indicated. Such a minimum heat of 
adsorption is shown in Titoffs observations on the adsorption of ammonia 
by charcoal, and in Chappuis’ results for the adsorption of sulphur dioxide 
by charcoal, etc. The author’s curve then passes through a maximum and 
drops to run parallel to the horizontal axis, with the heat of adsorption 
equal to the heat of condensation, as might well be expected whenp = P. 
The inflexion in the last portion of the curve occurs near a = 370, while in 
fig. 3 the inflexion is near a = 365, so there appears to be some close connec- 
tion between the final portion of the two graphs. 
We may regard the heat of adsorption as the sum of at least two effects, 
namely, loss of potential energy of the adsorbate in yielding to the attrac- 
* Mills, Journ. of Phys. Ghem ., x, 1 (1906), calculates a = 94‘7 cal. at -10° C. 
f Proc. Boy. Soc ., lxxviii, A, p. 412. 
