1908-9.] On the Reducing Action of Electrolytic Hydrogen. 91 
interval dt starting at the beginning of the time t, and k is the coefficient 
of the velocity of the action. From this equation the integral calculus 
enables us to find a relation between x and t, the corresponding values for 
any stage of the reaction, in terms of the original concentration and the 
velocity constant. 
This relation has the form, 
1 1 CL r 
— log = k. 
t L a - x 
It was observed that, if the amount of arsenic in the form of arsenic 
acid were increased in the cathode chamber, one arrived at a point 
when the cathode elements, which liberated no arseniuretted hydrogen 
under the ordinary conditions of the experiment, were capable of giving 
a small mirror on working the apparatus continually for 45 minutes, and 
the following Table shows the results : — 
Table III. — Elemental Arsenic in the Form of Arsenic 
Acid in 30 c.c. expressed in — 
1 
Units as above 
described. 
Millionths of 
a gramme. 
Nickel ..... 
20 
10-8 
Platinum .... 
90 
48-7 
Silver 
140 
75-8 
Palladium .... 
191 
103-5 
An attempt was made to measure the velocity of the reduction when 
using a copper cathode. No arseniuretted hydrogen was given off until 
the copper had become covered with a brownish -black deposit which gave 
by two analyses of small quantities the formula Cu s As. 
Chapman and Law found the same deposit, which they regarded as one 
of elemental arsenic. On making other experiments we obtained no deposit 
on the copper and no arseniuretted hydrogen evolved. 
With an electrolyte composed of 5 per cent, sodium hydrate solution we 
did get arseniuretted hydrogen evolved as follows : — 
Minutes . . . 24 5 74 10 12| 15 174 
Units obtained ..0 2 3 -5 2'5 2'5 1*5 1 = 13 
We tried the element magnesium as a cathode in a similar way to the 
other metals, but found it dissolved rapidly in the electrolyte whilst the 
current was passing. 
Table IV. shows the results of the different experiments, with the 
averages for each, also additions of the quantities evolved in each experi- 
