121 
1920-21.] The Adsorption of Gas under Pressure. 
additional quantity was separately determined for nitrogen and cocoanut 
charcoal and nitrogen and silica by methods which have previously been 
described (Briggs, loc. cit.). For each of the other gases and substances 
employed the addition in question was made by extrapolation from the 
graph itself. 
Fig. 1 records the results obtained with activated cocoanut charcoal, 
which, of all the substances tried, gave the greatest adsorption under 
pressure. Curves A and B respectively indicate for various absolute 
Fig. 1. 
A, Adsorption isotherm for nitrogen. 
B, Adsorption isotherm for hydrogen. 
C, Adsorption isotherm for nitrogen with damp charcoal. 
D, Simple compression according to Boyle’s law. 
E , Simple compression for hydrogen. 
pressures (abscissae) the total volumes (ordinates) of nitrogen and hydrogen 
contained by a gross volume * of 1 litre of charcoal. Gas volumes are 
expressed at N.P. and 15° C. To show the great influence of damp, a test 
was carried out on nitrogen, using cocoanut charcoal which had been for 
many months exposed to the air and which was found to hold 25 per cent, 
by weight of moisture. The results of that experiment are set forth by 
curve G. The straight lines D and E are included for the sake of com- 
parison ; the former expresses for 1 litre of open space the pv relation 
according to Boyle’s law, and the latter expresses that relation for 
hydrogen. 
* Gross volume includes the interstitial spaces, or voids, between the granules. 
