PRINCIPLES GOVERNING DIFFUSION OF GASES 179 



dioxide through tubes of known dimensions (Chap. XXI). They first made 

 the important discovery that if a septum which had been pierced with a small 

 circular aperture was interposed across a column of diffusing gas, that the 

 rate at which carbon dioxide diffused through this aperture was much greater 

 than the rate at which it passed through an equal area of the unobstructed 

 tube. 



Since the problem at present under consideration is the diffusion of water- 

 vapor rather than carbon dioxide through small apertures, the data presented 

 in Table 22 will be used to illustrate more fully the principles regarding 

 the diffusion of gases through small openings. These data were obtained by 

 sealing thin septa, through the center of which were cut round openings of 

 known dimensions, across the circular mouths of small bottles which had 

 previously been filled to a certain level with water, and then determining 

 the loss in weight of each bottle after all of them had been kept under 

 uniform conditions for the same period of time. 



TABLE 22 DIFFUSION OF WATER-VAPOR THROUGH SMALL OPENINGS UNDER UNIFORM 



CONDITIONS (data OF SAYRE, 1 926) 



The results of this experiment illustrate two important general principles: 

 ( I ) The quantities of water-vapor diffusing through small openings in a 

 given period of time are proportional (essentially) to the perimeters (cir- 

 cumferences) and not to the areas of the pores. This is shown by the close 

 correspondence of the figures in the last two columns of Table 22. (2) The 

 smaller the pore, the greater the water loss per unit area. The pore in 

 septum 2, for example, has an exposed area only slightly more than one-third 

 as great as the pore in septum i, but diffusion through it is nearly two-thirds 



