123 
1920-21.] The Adsorption of Gas under Pressure. 
Most commercial gas-cylinders are charged to 120 atmospheres; at that 
pressure the advantage to be gained by the charcoal is small. 
In fig. 2 a number of other pressure-volume isotherms are given, the 
ordinates in each case being the volumes (at N.P. and 15° C.) taken up by 
1 litre of the granules at 15° C. These, with the exception of B (nitrogen 
and common wood charcoal), are straight lines having much the same slope. 
The slope, moreover, is not far from 45°, which is that of the pv relation 
according to Boyle’s law. In some of the cases illustrated, for example 
Fig. 3. 
A , Including the gas compressed in the interstitial spaces. 
B, Corrected for the gas in the interstitial spaces. 
C, Simple compression according to Boyle’s law. 
A (oxygen and colloidal silica), the cylinder held slightly more than it 
would hold without adsorbent; while in other cases, such as C (nitrogen 
and birch charcoal), it held slightly less. In all these instances, then, the 
adsorption has been considerable ; in some it obeys Henry’s law, while in 
others it departs from that law. Curve A, fig. 3 (colloidal silica and 
nitrogen), expresses a relationship differing from Henry’s law ; it is 
analysed below. 
Tests made with firedamp compressed into anthracite threw fresh light 
upon the problem of sudden outbursts of gas in collieries, and that subject 
has been dealt with recently by one of us in a paper read before the 
Institution of Mining Engineers.* These outbursts, which occasionally 
* H. Briggs, “ Characteristics of Sudden Outbursts of Gas in Mines,” Trans. Inst . Min. 
Engs ., vol. lxi. 
