272 REPORTS ON INVESTIGATIONS AND PROJECTS. 



a small aperture. As they led to satisfactory values of the diffusion coeffi- 

 cient (i. e., grams of gas transpiring per second across an orthogonal square 

 centimeter, in case of a unit pressure gradient) of the imprisoned air through 

 water, and to a plausible value of the mean viscosity of the imaginary 

 medium within the molecular pores of the liquid through which a single 

 molecule of the gas virtually transpires, the investigation was taken up on a 

 more extended scale, for different pairs of gases. 



In Chapter II of the report the author has modified the diver in form and 

 the endeavor is made to obtain equal areas in the section of the cylindrical 

 swimmer and the annular space without, in order to conform more closely to 

 the equation of diffusion. The theory of the phenomenon and the errors 

 involved are carefully discussed. It appears that even for mixed gases the 

 volumes diffusing (not the masses) are always fully determinable. The ac- 

 curacy essentially depends on the measurement of absolute temperature and 

 of barometric pressure, and should therefore be of an order below 1/2730 per 

 o.i° C. or 1/7600 per 0.1 mm. of mercury. As the masses of gas contained 

 are usually much less than 10 — 2 gram, even in case of air, the weight less 

 than 0.000004 gram is determinable, showing the remarkable sensitiveness 

 of the method. Moreover, in the region of constant temperature the limit 

 of sensitiveness is immensely greater. 



To elucidate the phenomenon, experiments were begun with the transpira- 

 tion of imprisoned hydrogen into air, in which the resultant diffusion is 

 always unidirectional, outward from the diver. Initially rates as large as 

 5 mg. per day were obtained, which eventually decreased to values 100 times 

 smaller. Improvements of this experiment showed lower initial rates, de- 

 creasing to a constant value equivalent to a fixed diffusion coefficient. 



The diffusion of air into air through water proceeded with a definite mean 

 rate throughout the two or three months of observation, of about 32 X io — 6 

 grams per day, corresponding to the diffusion coefficient of 1.00 X io — 13 . 

 in c.g.s. units. But the daily march of the loss by diffusion was systematically 

 irregular, a result finally referred to the change of solubility of the gases in 

 water, with temperature. The consequence 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 ultimately the loss of weight of the diver was about 8.8 X 10 -6 grams 

 per day, corresponding to the diffusion coefficient 1.75 X io — 14 . 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 



