1908-9.] On the Reducing Action of Electrolytic Hydrogen. 95 
ment to show the total amounts obtained as adjudged from the estimations 
of the quantities represented by each mirror, when compared with standard 
mirrors produced by eliminating arsenic from arsenious acid by lead and 
by zinc cathodes each advancing by one unit of arsenic, as above described. 
Diagram 1 shows the elements whose supertensions were known to me 
arranged graphically as abscissse, the ordinates showing the amounts of 
arsenic liberated {a) from arsenious acid and ( b ) from arsenic acid in 25 
minutes from the different elements. 
Diagram 2 shows the average results obtained from the different 
elements examined, when acting on arsenious acid ; the ordinates repre- 
senting units of elemental arsenic, and the abscissae the time. 
Diagram 3 is similar to diagram 2, with the exception that arsenic 
acid was used instead of arsenious acid, and it is drawn on a smaller scale 
than diagram 2. 
Diagram 4 shows in one line the curve obtained by taking the 
average of the four elements, lead, zinc, cadmium, and tin, adding together 
the mirrors obtained in the first two periods of 2 \ minutes, and taking them 
as a 5-minutes interval, the others being taken at 2 J -minutes intervals. 
The other line shows the curve obtained by calculating x for the correspond- 
ing periods when using the mean constant, k showing that for these four 
metals the reaction is practically a unimolecular one. 
I have to acknowledge the services of my assistant, Mr L. L. Bircumshaw, 
for the perseverance and industry which he has exercised continuously 
during the last fourteen months in carrying out this investigation with me. 
(. Issued separately January 21 , 1909 .) 
