22 THE DIFFUSION OF GASES THROUGH 



If the correction for Stokes's law be introduced, :; must be replaced by 



i + 2?/r 



v = 



i+3^A 



where ^ is the coefficient of slip. If ^ = 7.6X io~^ an order of values given 



by Millikan {I. c), since 2r is but 3 X io~^, v is to be replaced by 2v/s. This 



makes 77 about 50 per cent larger, or the virtual viscosity of the medium is 



finally 



7/ = 2i8oXio~^ 



or about 11. 5 times as large as the viscosity of normal air. Finally, if the 

 correction for the density of glass given in §24 is inserted, this factor is 

 increased to about 13. 



20. Transpiration of Hydrogen into Hydrogen Through Water. — 



The behavior of hydrogen alone is peculiar. Hydrogen was imprisoned in 

 the swimmer, as usual, on the first day (see table 4). The upper surface 

 was still in contact with atmospheric air; hence the marked loss of weight, 

 the potential energy of separated gases being dissipated at the initial very 

 large rate. Thereafter, however, the air was replaced by an artificial 

 atmosphere of hydrogen from the gasometer, whereupon the large loss of 

 weight from February 25 to 26 almost at once changes to a gain, which in 

 its turn at first grows enormously, finally to decrease again to a smaller but 

 still persistent gain. This feature is probably due to the air dissolved in 

 the water (see fig. 7). Temperature modifies these data somewhat, but 

 the fact remains that hydrogen apparently diffuses through water, from 

 low to high pressure; i. e., up-hill or against the pressure gradient. This 

 is an interesting result, showing, like the first sudden drop, the importance 

 of the mixture effect. The potential energy of separated gases is being 

 dissipated at a rapid rate. Possibly some dissolved air at first diffuses into 

 the swimmer; but eventually hydrogen diffuses into it in excess of the 

 outgo of air; for in view of the pressure p^ of the diffused air within the 

 swimmer and since p^-^-pa is constant, p^ is less than the pressure B — iroi 

 the artificial atmosphere of hydrogen on top. The data after March 2 and 

 as far as March 9 show the trend of approximately 



w= 1.7 = io~®g/day or o.2Xio~^''g/sec. 



the result being a remarkably regularly increase of weight. One may note 

 that all these changes of direction are abrupt. Whether this is merely acci- 

 dental or whether certain definite mixtures diffuse together remains to be 

 seen. Unfortunately air is not a simple gas, so that the behavior of three 

 gases is really involved. 



A peculiar result during this stage of diffusion and occurring in all similar 

 cases is the enormous enlargement of microscopic air bubbles attached to 

 the solid surfaces wherever they are in contact with water. These are 

 sought out by the hydrogen, and soon become visible and greatly enlarged 



