856 Dr C. R. A. Wright on the Determination of 



when the electrodes are not of the same material, will be 

 considered in a future paper. 



93. Decomposition of Copper Sulphate with Copper Elec- 

 trodes, and of Zinc Sulphate with Zinc Electrodes, — The vol- 

 tameters used consisted simply of U-tubes filled with the hot, 

 just boiled, solution of zinc or copper sulphate employed, and 

 then closed by india-rubber stoppers through which passed 

 glass tubes with platinum wires through the drawn-out ends, 

 so as to make mercury-cups, and keei;> the solution from access 

 of air ; to the platinum wires were soldered the electrodes, 

 consisting of well-brightened strips of metal of known size, 

 the solderings and platinum wire being covered over with 

 gutta percha. By introducing a known resistance into the 

 circuit, composed of voltameter and electromotor (one or 

 more I)e la Rue, or other analogous cells), the current could 

 be regulated and measured, and hence the value of £ = E — CR 

 determined. In this way the following numbers were ob- 

 tained. With the copper-sulphate voltameter (which contained 

 a nearly saturated solution of the salt, containing 7*84 grammes 

 metallic copper per 100 cubic centims., the formula CuS0 4 

 36 H 2 requiring 7*80) the value of R was found to be close 

 to 110 ohms at the average temperature of the observations — 

 this number being calculated from the dimensions of the 

 column of fluid between the electrodes, and the specific resist- 

 ance of the fluid determined by a new method which will be 

 described in detail in a future paper. Similarly, the value of 

 R for the zinc-sulphate voltameter was calculated to be close 

 to 250 ohms. 



The following numbers were obtained with copper-sulphate 

 and copper electrodes : — 



Surface of each electrode = 8' 65 square centimetres. 



(I.) Values obtained when each electrode was new, i. e. polished 

 compact rolled copper plate. 





Microwebers 









Current, in 

 microwebers. 



per square 

 centimetre 

 of electrode 

 surface. 



E, in volts. 



CR. 



e=E-CR. 



71 



0-8 



•032 



•001 



•031 



14-6 



1-7 



•033 



•002 



•031 



23-8 



2-7 



•036 



•003 



•033 



30-8 



3-6 



•036 



•003 



•033 



35-7 



4-1 



•039 



•004 



•035 



73-0 



8-4 



•047 



•008 



•039 



1480 



17-1 



•060 



•016 



•044 



185-8 



21-5 



•062 



•020 



•042 



247-0 



28-6 



•073 



•027 



•046 



371-0 



42-9 



•088 



•041 



•047 



728-0 



84-2 



•131 



•080 



•051 



