at the Royal Institution, 1 900-1 907. 359 



that of the gas measured at 0"" and under a pressure of 760 mm. of 



mercury : — 



I. II. III. 



Volume Volume Ratio 



absorbed absorbed of 



at 0= C. at - 185° I. to II. 



2 c.c. 15 c.c. 7-5 



4 135 34-0 



12 150 12-5 



12 175 14-6 



15 155 10-3 



18 230 12-8 



21 190 9-0 



Heliiun . 



Hydrogen 



Electrolytic gas 



Argon 



Nitrogen 



Oxygen . 



Carbonic oxide 



Carbonic oxide and oxygen 30 195 6 • 5 



These observations were made at an early stage of the inquiry. 

 Afterwards it was found that the quality of the charcoal depends 

 much on the way in which it is prepared and that the absorptive 

 power is enhanced l^y carbonising the cocoanut shell slowly at a 

 gradually increasing temperature ; whereas the specimens at first 

 used absorbed only about 150 c.c. of air per gramme at - 185,° 

 those prepared subsequently with these precautions absorbed from 

 350 to 400 c.c. per gramme. Porous materials other than charcoal, 

 such as ahimina, meerschaum and silica, also absorb an increased 

 proportion of gases at low temperatures but their retentive power is 

 much inferior to that of charcoal, which clearly has a special power. 



Pressure has but relatively little influence in increasing the 

 amount of gas absorbed. Thus in one case it was observed that 

 6 • 7 grammes of a particular specimen of charcoal would not absorb 

 more than 1 litre of hydrogen, even when the pressure was raised 

 from 10 to 25 atmospheres, the amount taken up having reached a 

 limit at the lower pressure and being then less than double what it 

 was at ordinary atmospheric pressure. 



Absorption of a Mixture of Gases hy Charcoal. — One of the most 

 interesting series of observations made is that relating to the equi- 

 libria established on saturating charcoal at low temperatures with a 

 mixture of gases. Charcoal which has been heated, exhausted and 

 then allowed to absorb ordinary air at —185° presumably contains 

 within its pores a mixture approximately of the composition repre- 

 sented by Fig. 1. 



If, at the same low temperature, a stream of air be passed slowly 

 and continuously over the charcoal, at first almost pure nitrogen 

 escapes, showing that the system has a preference for oxygen ; after 

 several hours, however, the occluded gas has a new and apparently 

 definite composition. On displacing the whole of the gas from the 

 charcoal, a mixture is obtained containing on the average about 

 60 per cent, of oxygen, corresponding nearly to Fig. 2. 



If the charcoal saturated with such a mixture be subjected in a 

 similar manner to the action of a slow current of hydrogen, about 



