1 8 THE DIFFUSION OF GASES THROUGH 



It follows therefore, initially, when p^ = U-\-p' or pa = o, there being a 

 charge of hydrogen only, 



W/v= 00 



for all reasonable values of p}^ and v. Hence diffusion, to keep pace with the 

 loss of potential energy per second, should be extremely rapid at the outset. 

 The observations below, as a rule, show enormously rapid transpiration 

 at the beginning of the experiment, which thereafter rapidly diminishes and 

 is often reversed in the lapse of time. There can be little doubt, therefore, 

 that in the cases of mixed gases the rate at which the potential energy of 

 the system diminishes may be invoked to interpret the observed phenom- 

 enon, particularly when the diffusion take place, on the whole, against the 

 gradients due to the water heads. Beyond this, however, i. e., further than 

 as a means of pointing out the source of energy, the potential energy of 

 separated gases will not probably need to be considered. 



19. Transpiration of Air into Air Through Water. — ^Tentative results of 

 this kind were given in the preceding chapter, from observations lasting a 

 period of about eleven years. The swimmer was unsuitable for the purpose, 

 but the datum found, k = 2.gXio~^^, should furnish an estimate as to the 

 probable order of values to be anticipated. 



In table 3 I have given the present results, so far as they have matured, 

 showing the daily diminution of the mass {m in grams) of the imprisoned air. 



Figure 6 contains the value of m in milligrams on successive days. As 

 the observations can not be in error, even as much as o.i per cent, the 

 marked discrepancy encountered must have some real cause. True, the 

 opportunities for constant temperature were not at hand and there is inter- 

 ference with the gradient due to convection, in the case of an apparatus 

 like fig. 3 ; but the actual increase of weight can not apparently be referred to 

 these causes, except in so far as m = m' pi p^ , in equation (5). There are two 

 other explanations : If the temperature of the column of water is not exactly 

 that of the environment during observation there will be eddy currents, 

 which will raise and depress the swimmer by friction with its sides. This 

 was actually tested on February 27 by artificially heating the apparatus 

 from without. The swimmer is then too heavy, due to a downward axial 

 current and the charge of air found too small. The discrepancy, however, 

 is inadequate in amount. The predominating cause seems to be associated 

 with the effect of temperature on the solution* of gases in water. At higher 

 temperatures gas is evolved from the water and caught by the swimmer 

 and the imprisoned air is therefore too hea\'y. At lower temperatures the 

 gas of the swimmer is absorbed into water and the charge of air is too light. 

 As this effect is inherent in the experiment itself, there is no way of com- 

 bating it except the maintainance of absolutely constant temperature. 

 The coefficients will eventually have to be computed by the method of 



*The final curve for the hydrogen-hydrogen system is much smoother than the 

 corresponding curves for mixed gases under the same conditions. Hence the pref- 

 erence given to the solution effect. 



