DIFFUSION OF GASES THROUGH PORES 95 



which determines the relation of the size of the pore to the 

 diffusion rate. 



It is clear, therefore, that if instead of a single pore, the 

 septum through which diffusion takes place is pierced by a 

 number of small openings, much higher rates of diffusion 

 will occur than through a single opening with an area equal 

 to the combined areas of all the pores. Browne and 

 Escombe demonstrated this by using celluloid septa pierced 

 with different numbers of pores set at different distances 

 apart. Their results are given in Table XXIII, 



TABLE XXIII 



Diffusion of Carbon Dioxide through a Multiperforate Septum 



Average area of tubes employed, 9*39 sq. cm. 

 Diameter of each perforation in septum, 0*38 mm. 



From this it appears that when the septum is pierced 

 by about 1000 pores, the combined area of which is 11*34 

 per cent, of the area of the septum, the diffusion is 56 per 

 cent, of that taking place with no septum present ; while 

 with only 26 pores, having a combined area of 0*3 1 per cent., 

 the diffusion is 14 per cent., that is, nearly fifty times what 

 could be accounted for by the available area. 



When the pores are close together they interfere mutually. 

 This may be most easily understood by taking the case of 

 transpiration. The water vapour leaving one stoma meets 

 with that leaving its neighbours before it has fallen to the 

 vapour pressure in the atmosphere, and the rate of flow is 

 thereby reduced. The last column shows the theoretical 



