2(H) Dr. 0. lv. A. Wright on the Determination of 



of the cylinder and including that of the piece of platinum 

 wire connected with it to make contact) 27*5 square centims. 

 Average bore of U-tube between the electrodes round the 

 bend =1*50 square centim. in section. Distance apart of 

 centres of cylindrical electrodes = 13 - centims. 



Limiting value of current, expressing the rate of diffusion 

 discharge not seriously increased by effects of variation of 

 temperature ; =4*0 microwebers, capable of evolving about 

 0*04 cubic centim. of hydrogen at 0° and 760 millims. in 24 

 hours. 



Voltameter No. 2. Similar electrodes, each exposing 8'0 

 square centims. of total surface. Centres of electrodes 8*0 

 centims apart. Average bore of tube 1*0 square centim. in 

 section. 



Limiting value of current 8*0 microwebers. 



Voltameter No. 3. Electrodes of foil, each exposing 3*2 

 square centims. total surface. Centres of electrodes 6 centims. 

 apart. Average bore 1*1 square centim. 



Limiting current-value 5*0 microwebers. 



Voltameter No. 4. Electrodes of platinum wire, each ex- 

 posing 0*19 square centim. of total surface. Distance apart 

 17 centims. Average bore of tube O08 square centim. 



Limiting current-value 1*5 microweber. 



Voltameters Nos. 1, 3, and 4 contained acid of which 100 

 cubic centims. contained 27*0 grammes of H 2 S0 4 . In these 

 three cases the values of the limiting currents are evidently 

 iu the order of the facility with which diffusion would go on — 

 the column of fluid between the electrodes being respectively 

 13, 6, and 17 centims. long, the first being widest and the 

 last narrowest, whilst the current values are respectively 4*0, 

 5*0, and 1*5 microweber. The relatively larger value for the 

 limiting current of voltameter No. 2 is explained by the fact 

 that it contained a more dilute and consequently less viscid 

 acid, 100 cubic centims. containing only 1*0 gramme of H 2 S0 4 . 



The amount of current due to imperfect insulation of the 

 voltameter &c. in these experiments was wholly inappreciable. 

 On connecting the voltameter emptied of acid with a battery 

 of two or three Minotti cells and a resistance of 100,000 ohms, 

 no leakage-current at all could be detected ; that is, the dif- 

 ference of potential between the ends of the resistance of 

 100,000 ohms was less than *005 volt (half a scale-division of 

 the quadrant-electrometer); so that the leakage-current was 



•005 x 10 8 

 less than ■,.,." , i/t/> — r— „, i. e. less than 0*05 microweber, a cur- 

 100,000x10^ ; 



rent which would require upwards of five years to evolve 



1 cubic centim. of hydrogen from water. 



