UQUIDS AND AIvUKD IjXPIvRIMENTS. 



87 



content of the diver, the result would be nil in the lapse of time, supposing 

 there is no continuous mean rise or fall of temperature, the latter in its 

 effects being indistinguishable from diffusion. The issue in question, 

 however, is the change of com.position of the imprisoned air, which becomes 

 either relatively rich or poor in oxygen; and this modifies the gradients 

 correspondingly. Any change of barometric pressure, nlorco^'er, is felt in 

 the gas inside and outside of the diver at once, but it does not follow that 

 it is also felt in the pores of the liquid. There will probably be diffusion 

 out of and into the pores of the liquid as the barometer falls and rises, 

 respectively, at a slow rate and thus not easily observable. The presence, 

 finally, of any absorbent of a gas within the liquid, as, for instance, the case 

 of bright copper, may confuse the result. 



Finally, the discrepancy between the results obtained in a closed manom- 

 eter in the lapse of years and the above results with the diver in the lapse 



Fig. 38. — Chart showing variation of volume coefficients of 

 diffusion at standard pressure and temperature with 

 composition and density of solution. 



of months must be considered. These experiments have been in progress 

 for so short a time, relatively speaking, that all interpretation is merely 

 tentative. It would not be consistent if carried into detail. Nevertheless, 

 if we suppose the gas contained in the pores of a liquid to be relatively fixed, 

 then the presence of convection currents due to gradual changes of temper- 

 ature on the outside of the apparatus would carry the more compressed gas 

 of the lower level to the free surface, and conversely. Such an effect, whicli 

 is equivalent to an increase of gradient, being absent in the narrow tube of 

 the manometer, diffusion should be slower in the latter case, as it appears 

 to be. Here, however, the identity of the small amoimt of gas in the two 

 shanks of the U-tube is in question. 



If the results of table 46 be graphically represented for each solution, so 

 that the coefficient of diffusion may appear in its variation with the strength 

 of solution, the sets of curves given in fig. 38 will exhibit the chief content 

 of the table. From these curves it appears that the diffusion of a gas in 



