414 On Measurements of Electromotive Force fyc. 



Interpolated resistance, Calculated resistance 



stated in ohms. of rest of circuit. 



10 and 20 ... . 10'3 ohms. 



10 „ 15 ... . 10-0 „ 



10 „ 5 . . . . 10-3 „ 



5 ,, . . . . 9-9 „ 



This gives as the resistance of the circuit, 10*12 ohms. 

 Adding this number to the interpolated resistance in each 

 experiment, and calculating the E.M.F. of the circuit for each, 

 we get as the mean, 1*084 volt. The number obtained on the 

 electrometer was 1*076 volt. 



After these measurements were completed, the current was 

 allowed to run through the galvanometer for nearly two hours. 

 The deflection remained very steady, slightly increasing and 

 then slightly diminishing. At the end of this time the deflec- 

 tion corresponded to a current of *1068 ampere. On again 

 interpolating resistances, the following results were obtained: — 



Interpolated resistance. Calculated resistance. 



and 5 10-1 



5 „ 10 9-9 



10 „ 15 10-0 



Mean .... 10*0 ohms. 



The E.M.F. calculated from these results is =1*067 volt. 



The E.M.F. on the electrometer amounted to 1*072 volt, a 

 number about as much higher as the first number was lower 

 than that calculated from the current measurements. 



Experiments are evidently capable of being made of far 

 greater accuracy than these, but they are sufficient to show 

 that the E.M.F. of the cadmium-iodine cell as measured on 

 the electrometer is really due to the formation of cadmium 

 iodide. 



Similar experiments should, I feel sure, be made for all 

 cells which are not well known, before any attempt is made 

 to base important conclusions on the differences between the 

 calculated and measured E.M.F. 



As already stated, the area of the plate used amounted to 

 10*6 square centim. Probably one side of the plate supplied 

 most of the current ; but, considering the current as equally 

 shared between both sides, this means *01 ampere per square 

 centim. of surface steadily supplied for two hours, about 500 

 times what could have been drawn from the cell with sta- 

 tionary plates, without causing a serious fall in E.M.F. 



