Manchester Me?noirs, Vol. Ixi. (191 7) No. 9 



IX. Recent Work on Overvoltage. 



By Dr. E. Newbery. 

 {C ommunicated by Professor A. Lapzvorth, D.Sc, F.R.S., F,I,C) 



Read May 8t/i, igiy. Received for Publication May 22nd, igij. 



Since the author's last communication to this journal, ^^ a 

 considerable amount of further work has been carried out on the 

 same subjecjt, and certain facts have come to light which neces- 

 sitate some modification of the theory then proposed. 



This work has bieen done along three Unes — 



r. (Measurement of cathodic oyervoltages of metals and 

 alloys i|n dilute acid ,and in alkali, under varying conditions of 

 time and current density, hydrogen being liberated in all cases. 



2. Measurement of anodic overvoltages under similar con- 

 ditions, oxygen being liberated. 



3. 'Measurement of " metal " overvoltages during electro- 

 lytic deposition or dissolution of a metal in a solution containing 

 a salt of that metal. 



Altogether about 12,000 measurements have been made 



partly with the objeqt of supplying a broad basis on which to 



found a theory of overvoltage, and partly to supply data which 

 will be generally useful in edectrolytic work. 



In the following tables current densities in milliamperes per 

 sq. cm. are given in the first column. Columns headed A. ghow 

 the first sets of rteadings obtained witli the given electrodes 

 immiediately after immersion in the electrolyte, whilst those 

 'headed B.: show the averages of at least four sets taken subse- 

 quently. By comparing the two columns, the combined effect 

 of tinae and subjection to a high current density may be 

 observed, whilst further information as to the effect of time 

 alone may be obtained from the later tables. 



T'he test electrode was in all cases a rod or strip of metal 

 having an exposed surface of i sq. cm., and the secondary elec- 

 trode was a sheet of platinum, 10 sq. cms. area, except when 

 measuring metal overvoltages, when a similar sheet of the metal 

 under examination was used. 



* Vol. 60 (1916), No. II. 



Decemder ijth, IQ17. 



