354 Dr. C. E. A. Wright on the Determination of 



microwebers to pass for two or three days the values of e 



became approximately steady ; the following numbers were 



obtained, the electrodes being 13 centimetres apart and the 



bore of the U-tube between them 1*09 square centimetre, so 



13 x 2*5 

 that the value of R= — =30 ohms, 2*5 ohms being (as 



calculated in § 89, footnote) the specific resistance of sulphuric 

 acid of 11*4 grammes per 100 cubic centims. The values of 

 E are all probably a little underestimated, because it was 

 found impossible to allow a current of 25 to 50 microwebers 

 to pass for a fortnight, so as completely to saturate the acid 

 round the — electrode and the electrode itself with hydrogen, 

 and get rid of the last traces of dissolved oxygen, as was done 

 with platinum, carbon, or gold electrodes; for before a fortnight 

 had elapsed, the copper dissolved from the + electrode and 

 converted into copper sulphate had diffused to the other 

 electrode and became partly re-deposited there (at least this 

 phenomenon was observable in less than a fortnight when a 

 polished platinum plate was used instead of a copper one for 

 the — electrode). Probably this source of error affects all the 

 observations about equally, and is but slight, since sensibly the 

 same values of E were observed for a given current whether 

 the observations were made on the 4th or on the 9th day. 





Microweber per 









Current, in 

 microwebers. 



square centi- 

 metre of elec- 

 trode surface. 



E, in volts. 



CE. 



e=E-CK. 



9-7 



114 



•523 





•523 



20-1 



2-34 



•548 



•ooi 



•547 



49-8 



4-23 



•586 



•001 



•585 



77-1 



9-06 



•600 



•002 



•598 



108-7 



12-4 



•616 



•003 



•613 



174-7 



20-5 



•669 



•005 



•664 



226-0 



26-6 



•685 



•007 



•678 



378-0 



44-5 



•720 



•011 



•709 



These numbers clearly show that the values of 7/ + (1 — fti) 

 Hx—w-iAi for currents of not less than 1*14 microweber per 

 square centimetre of electrode surface are positive, and in- 

 crease as the current increases ; for h fr cannot exceed 0*4 

 volt, and the sum of h f/ and // + (1— n^YL-^— nj^is uniformly 

 greater than this. [That li ,f is not >0*4 volt results from the 

 valuations of E 3 cited in Part I. § 21 and 22, deduced from 

 the experiments of Favre, Julius Thomsen, and Raoult, 

 which varied between 1*162 and 1*321, being uniformly 

 above 1*1 volt, so that, as E^l'50 volt (Part II.), h r/ =B 1 

 — E 3 cannot, exceed 0*4 volt.] This increase is mainly due 

 to the decrease in value of n\ as the current increases ; for 



