406 MK. T. GRAHAM ON THE ABSORPTION AND 



nitrogen observed ; for the former gas has a tendency to flow back again to the external 

 atmosphere when the hydrogen becomes small in volume ; and the proportion of oxygen 

 becomes eventually no higher than 21 per cent, of the whole gases remaining in the 

 balloon, including the hydrogen. Thus after six hours the proportion of oxygen was 

 33-03 to nitrogen 66-37 volumes, and after twenty-four hours oxygen 26-48 to nitrogen 

 73-52 volumes, the hydrogen constantly diminishing at the same time. 



The entrance by infiltration of atmospheric air into a balloon of rubber inflated with 

 carbonic acid gas brings us still nearer to a practical dialytic separation, as the carbonic 

 acid can be withdrawn entirely by means of caustic alkali, after a certain time has 

 elapsed, and the infiltered air enriched with oxygen be dealt with by itself. A balloon 

 containing carbonic acid, when placed in the atmosphere, was reduced in four hours 

 from 160 to 90 millims. in diameter, and it had now acquired 199 cub. centims. of gas 

 not dissolved by alkali. This gas was capable of reviving the combustion of wood 

 burning without flame, and was found to consist of 



Oxygen 37-1 vols. 



Nitrogen 62-9 „ 



100-0 



To produce this concentration of oxygen, it is quite necessary that the operation be 

 interrupted at an early stage, as was done in the last experiment ; otherwise the oxygen 

 diminishes again in proportion to the nitrogen, falling at last to the normal proportion 

 of 21 per cent, as in the external air. Thus a balloon inflated by carbonic acid to 150 

 millims. in diameter, was found to lose nearly all its carbonic acid in the course of 

 twenty-four hours. It gave 150 cub. centims. of gas after treatment with caustic potash. 

 This was air of the composition, 



Oxygen 22-6 



Nitrogen 77-4 



100^ 



and exhibited therefore no material augmentation in the proportion of oxygen. 



It may be inferred, from the familiar fact that air dissolved in water contains so high 

 a proportion as 30 per cent, of oxygen, that if carbonic acid gas were divided from 

 atmospheric air by a film of water, the former gas would come to be charged through 

 the film with air bearing the same high proportion of 30 per cent, of oxygen. But it 

 is not easy to imitate this experiment unless the dividing film is supported by a 

 membrane of some sort. The air from the atmosphere, which entered a fresh ox-bladder 

 preserved humid and inflated with carbonic acid, was found to possess 24-65 per cent, 

 of oxygen to 75-35 of nitrogen, which is but a small increase in the proportion of 

 oxygen. But the thickness of the membrane here was too great, and other circumstances 

 of the experiment were unfavourable. 



A balloon of rubber inflated to 150 millims. in diameter with carbonic acid was 



