8 



THE DIFFUSION OF GASES THROUGH 



accurately measured. Finally, the whole arrangement is more conducive 

 to constancy of temperature in the essential parts of the apparatus than is 

 the case in fig. 3. 



1 1 . Imprisoned Hydrogen Diffusing into Free Air. Preliminary Data. — 



As before the mass m' of hydrogen contained at v in the swimmer is given by 



m 



Mgp^ H 



R 



T \p,n Pn/ 



(l) 



where Mg is the weight of the glass swimmer, p„ the density of mercury at 

 0° C, p„ the density of water at /°, and Pg the density of glass. H is the 



barometric height diminished by the head equal to 

 the vapor pressure of water vapor, r the absolute 

 temperature, and R the gas constant of hydrogen. 

 The latter applies at the outset onl)^ Since 



M= 18.09 grams p„= 13.6 



g = 98i 

 the constant A = Mgp^/R 



7^ = 41.4X10'' 



0.005823. The hydro- 

 gen used was obtained electrolytically from water, 

 enough being introduced into the swimmer to just 

 prevent flotation. 



In the course of time the gases contained in the 

 diver will change from the influx of diffused air and 

 the efflux of hydrogen. Hence the gas constant R 

 of the imprisoned gas is not fixed in value. Sup- 

 posing, however, all observations to be made or all 

 diffusion to occur at a certain mean pressure B and 

 temperature t; since for all gases Rp = RoPQ, the 

 latter referring to the initially pure gas at the given 

 temperature and pressure (supposed, as stated, to 

 be constant during flotation); and since, finally, 

 PI = v'p' = vp, during and before flotation, therefore 



RoPo T ^Pto Pg^ ^Pw Po^ ^ 



Fig. 5. — Loss of mass 

 of gas in diver in lapse 

 of days. Diffusion of 

 hydrogen into air. 



dO 



so that the variations of volume v are referred to in taking the quantity 

 A = MgpjR constant. To pass from v to the mass m it will be necessary to 

 multiply A by p/p^ where the density p of the imprisoned gas is not known. 

 I shall suppose that the variation of temperature and pressure during a long 

 period may be eliminated by the method of least squares. Hence only the 

 coefficients of diffusion by volume, called k below, are determinable. The 

 coefficient of diffusion by mass, k, can not, apparently, be found at once, 

 except for a system of but one gas. 



Table 2 contains the observations made preliminarily with hydrogen, in 

 so far as they are trustworthy. These and others are reproduced in fig. 5, 



