n PREFACE. 



perature. The result of this is absorption and release of gas as temperature 

 falls or rises, respectively, during the occurrence of the otherwise steady 

 diffusion. In the long series the temperature effect was eliminated by the 

 method of least squares. 



Much more striking were the phenomena encountered in endeavoring to 

 find the coefficient of diffusion of hydrogen through water into hydrogen — in 

 which, however, the ultimate daily loss of weight of the diver became con- 

 stant, corresponding to the diffusion coefficient of hydrogen alone. Referred 

 to molecular conditions, the molecule can be regarded as moving through a 

 medium about 15 times as viscous as ordinary hydrogen, whereas in case of 

 air the medium would be about 13 times as viscous as air. The daily march 

 of results in the hydrogen observations was most striking, inasmuch as the 

 diver first lost weight at an initially enormous rate for two days, then 

 rapidly gained weight at a decreasing rate during the ensuing ten days, and 

 thereafter assumed the steady rate of loss for months. Changes of this 

 nature are, as a rule, abrupt. It was found that a similar doubly inflected 

 progression of results usually occurs unless all manipulations at the outset 

 are conducted not in air, but in a medium of hydrogen, or in general of the 

 identical gas within the diver. Otherwise the imprisoned gas is at once con- 

 taminated by diffusion of the surrounding gas into it. 



It is not, perhaps, fully appreciated by chemists that gases, otherwise 

 pure, if stored over water, at once lose purity in consequence of air by 

 diffusion. In fact a gas. A, in the swimmer, in presence of gases, B, C, etc., 

 can not escape by diffusion until the sum of the partial pressures, B, C, etc., 

 is equal to or greater than the pressure equivalent of the head of water under 

 which the gas A is submerged. Before that the gas of the environment will 

 diffuse into the diver against the hydrostatic pressure of the head of water, 

 i. e., apparently up hill. The same explanation accounts for the enormous 

 inflation of the microscopic air bubbles, for instance, in the liquid, when the 

 surrounding atmosphere is some other gas, like hydrogen; also for the 

 bubbles which still appear and grovv' at rough points of a surface after the 

 effervescence of a compound gas has ceased. 



Other diffusion experiments, air into hydrogen, oxygen into hydrogen, 

 hydrogen into air, etc., were eventually pursued through months and com- 

 pleted in a similar manner and with similar results. The graphs obtained 

 are throughout striking. It is feasible to derive the differential equation 

 for these phenomena, but, as might be expected from the complications in 

 question, it could not be integrated. Finally, it is interesting to note that 

 if the diffusion coefficients are given, the densities of the gases diffusing at a 

 constant rate may be computed ; or, from another point of view, the degree 

 of purity of the gas so diffusing may be ascertained. 



The sensitiveness of weighing in case of the Cartesian diver, where the 

 whole apparatus is quite submerged in water or some other liquid and capil- 

 lary forces are out of the question, naturally suggested the application of this 

 method for the measurement of high potentials in case of the absolute elec- 



