Chemical Affinity in terms of Electromotive Force. 349 



This effect, however, is partly due to the considerable increase 

 in effective surface thereby occasioned. In order to see what 

 effects would be produced by substituting polished gold or 

 compact carbon for polished platinum, the following experi- 

 ments were made : — The carbon electrodes were thin slabs 

 about 1-2 millimetres thick, sawn from hard rods used for 

 electric lights ; they were were filed to a tolerably smooth 

 surface, and digested for some months with aqua regia — also 

 boiled at intervals with hydrochloric, nitric, and dilute sul- 

 phuric acids. To make connection with the battery, the upper 

 portions were wrapped round with platinum foil tightly tied 

 on with platinum wire, connected to the glass mercury-cup 

 supporting the electrodes ; the whole of the platinum foil and 

 wire was then covered with gutta percha, so that only carbon 

 was exposed to the liquid in the voltameter. To make sure 

 that as little as possible of metals &c. capable of being acted 

 on by nascent electrolytic oxygen was present, they were used 

 as + electrodes for several days in the electrolysis of dilute 

 H 2 S0 4 , such a current being employed as to keep a con- 

 tinuous evolution of gas at the rate of some 50 to 100 cubic 

 centims. of hydrogen per day. The superficial area of each 

 electrode (measured by scale and compasses, and making no 

 allowance for increase of surface due to the carbon being 

 slightly pitted and not smooth) was 3*9 square centimetres. 



The gold electrodes were similarly mounted, a platinum 

 wire being fused to them, and the surface of the platinum 

 covered with gutta percha, so that only gold was exposed to 

 the liquid in the voltameter. Surface of each electrode = 17-0 

 square centimetres. 



Values obtained with Acid containing 27 grammes per 100 cubic 



centims. 



Gold Electrodes. 

 The distance apart of the centres of the electrodes was 15 

 centimetres, and the bore of the tube between them l'l square 



centimetre : so that R = — ^7j — = 19'1 ohms. 





Microwebers per 









Current, in 

 microwebers. 



! square centi- 

 metre of elec- 

 trode surface. 



E, in volt?. 



OR 



<?=E-CR, 



9-8 



0-58 



2-139 





2-139 



147 



086 



2-312 





2-312 



340 



200 



2-407 



•001 



2-406 



55-7 



3-27 



2-452 



•001 



2451 



156-9 



9-23 



2-515 



•003 



2-512 



3640 



21-4 



2-627 



•007 



2620 



668-6 



393 



2-701 



•013 



2-68S 



