162 



PHYSIOLOGY OF NUTRITION. 



Hydrogen, and then rapidly inverted under water, the fluid 



quickly ascends to a considerable 

 height in the apparatus, since in 

 a given time a larger quantity of 

 Hydrogen passes through the clay 

 into the atmosphere than atmo- 

 spheric air into the tube. 



It is more convenient to work 

 with the apparatus represented in 

 Fig. 55, which I also used. The 

 disc of clay T closed the upper end 

 of the glass tube G, which at the 

 bottom dips into water. The stop- 

 cock H being open, Hydrogen is 

 led into the apparatus through S. 

 On closing the stopcock again, the 

 water gradually rises in the tube 

 G. This arrangement may also be 

 employed for many of the experi- 

 ments which follow. 



Carbon dioxide having a high 

 specific gravity traverses porous 

 septa, such as plates of clay, at all 

 events much more slowly than 

 atmospheric air; but the very op- 

 posite is the case, if we separate 

 the Carbon dioxide from the at- 

 mospheric air by a septum com- 

 posed of a substance which exerts 

 a specific attraction (gas absorp- 

 tion) on the Carbon dioxide. I. closed a glass tube with a thin 

 rubber membrane (fastened on with a piece of elastic), filled the 

 tube with Carbon dioxide, and inverted it under mercury. The 

 mercury gradually rose higher and higher in the tube. It is true 

 the mercury does not rise rapidly, and it is hence necessary to keep 

 the experiment going for a good time (say twenty- four hours). 

 If it is not desired to make accurate quantitative experiments, but 

 merely experiments for demonstration purposes, it is well to have, 

 in addition to the tube closed with the rubber membrane, another 

 of the same dimensions, but fused up at its upper end. The 

 position of the mercury in this second tube indicates how far the 



FIG 55. Apparatus for investigat- 

 ing the diffusion of gases. 



