ROSA. VINAL, AND McDANIEL: SILVER VOLTAMETER 57 



bowl and connected the electrolyte in this thru a siphon to a 

 second bowl serving as cathode. First we measured the pro- 

 gressive change in acidity of the anode solution as electrolysis 

 took place and found that practically no change of acidity occurs 

 until the silver on the anode was reduced to about 0.5 gram after 

 which it rose very abruptly. Next we measured the potential 

 difference between the anode and an intermediate electrode and 

 found this also constant until about 2.5 gram of silver remained. 

 We then examined the question quantitatively as follows: 



WEIGHT OP SILVER 

 ON ANODE BOWL 



grams 



8 



DEPOSIT IN 

 CURRENT ' LOSS AT ANODE ! GAIN AT CATHODE ' STANDARD 



I I VOLTAMETER 



amp. mg. \ mg. mg. 



0.500 2164.81 1 2164.78 I 2164.81 



9 I 0.500 , 2092.12 2091.92 ^ 2091.83 



* ' 



The results show a surprising agreement. These were made 

 using a pure crystalline deposit for the anode. With a striated 

 deposit made from a filter paper contaminated solution the result 

 was very different. The anode turned dark and had a very large 

 amount of slime all of which was collected and added to the bowl. 

 The results using a pure solution and this impure anode are as 

 follows : 



Anode lost 2095 .43 mg. 



Cathode gained 2092 .21 mg. 



Standard voltameter 2091 .83 mg. 



The conclusion leaves no room for doubt that the purity of the 

 anode is essential in such an experiment and this should be con- 

 sidered in voltameter work in general. 



We have added to our complete paper a further discussion of 

 the volume effect (see Part III) in reply to von Steinwehr's criti- 

 cisms. (Zs. f. Instr., November, 1913) we have shown that this 

 phenomenon of excess deposit in large bowls over small bowls, 

 when impure electrolyte is used, is not confined to the porous cup 

 form as von Steinw^ehr asserts, but has been observed in the filter 

 form by Schuster and Crossley and in the siphon and Smith 

 forms by ourselves. We have overcome this troublesome volume 

 effect by purifying the electrolyte. We wish to lay great stress 

 on the purity of the electrolyte used in obtaining the results 



