2G4 Dr. C. R. A. Wright on the Determination of 



supporting I was firmly fixed, and then the cork H. If 

 now the two electrodes were connected with a battery, evi- 

 dently the gases evolved would arise, the one into the bell- 

 mouth of this capillary tube, the other to the surface of the 

 fluid in the longer limb, B, of the upper U-tube. By making 

 K the — electrode, and by working the glass rod I up or down 

 through the cork supporting it, the hydrogen evolved could 

 cither be drawn over into the measuring part EF, or forced 

 back again into D: and in this way measurements of the gas 

 contained in D could be readily made. When the quantity 

 of gas collected became too large for measurement, it could 

 be drawn completely over into the lower U-tube, G, so as to 

 empty the bell and capillary tube of gas, by simply drawing 

 out the rod I. 



79. In order to saturate the acid in the two limbs A and B 

 with hydrogen and oxygen respectively, as well as to do away 

 with the sources of loss of hydrogen due to traces of residual 

 air and occlusion by the electrode K, a weak current (about 

 •0000025 to -C00005 C.G.S. current-unit*, capable of evolving 

 from about 0*2 to 0*5 cubic centim. of hydrogen per day) was 

 passed through the apparatus for several days or even two or 

 three weeks, the evolved hydrogen being from time to time 

 drawn over into the lower U-tube Gr, and expelled by 

 cautiously loosening the cork H for an instant or two. If 

 during this time measurements were made of the quantity of 

 hydrogen actually collected as compared with that calculated 

 from the current passing (kept as nearly as possible uniform 

 by suitably altering the resistance in circuit, and measured by 

 determining the potential difference set up between the ends 

 of that resistance, as described in Part III. § 69), it was found 

 that a deficiency in the amount collected was always observed, 

 but that that deficiency gradually decreased to a constant mini- 

 mum. Moreover the period when this constant minimum 

 was first reached was found to be precisely the period at 

 which the rate of loss of polarization observed on breaking 

 circuit reached its constant minimum (Part III. § 70) ; and 

 it was also precisely the period when the counter E.M.F. set 

 up by a given current with a given apparatus ceased to increase 

 (§ 85). These coincidences, as well as a priori reasoning, 

 leave no room for doubt that the cause of the residual constant 

 discrepancy between the observed and calculated amounts 



* The currents used in the majority of the experiments described below 

 being only small fractions of a weber, it is more convenient to measure 

 them in millionths of a weber, or microwebers. One niicroweber 

 = 0-000001 weber = -0000001 C.G.S. current-unit ; so that the above 

 currents are respectively 25 and 50 microwebers. 



