396 Prof, Skinner on the Relation of Electrode Fall 
fall with use, the conclusion is warranted that here, as in 
hydrogen, the unchanged values are the true ones. On the 
other hand, nitrogen gives for all metals a greater fall at the 
higher pressure, there being an increase of about 3 per cent. 
in the fall with a 30 per cent. increase in the gas-pressure. 
This is smaller than that previously reported, yet the question 
as to the change with gas-pressure in nitrogen must still 
remain unsettled. For the present investigation, however, 
the above results at least show the anode series, like the 
cathode series, to be independent of the gas-pressure and 
current-density under which it may be obtained. 
The Electrode Series. 
In Hydrogen.— Observations were first made on the cathode. 
Using metals representing the contact series, preparations as 
already described were carried out. To facilitate the rapidity 
with which observations of the electrode fall were made, the 
contact-brush (B, fig. 1) was so arranged that the discharge 
could take place from the next metal used just before the 
circuit from the preceding one was broken. By this device, 
the current through the tube remained uninterrupted during 
the series of observations, and oscillation of the electrometer- 
needle avoided. This arrangement allowed the cathode-fall 
to be obtained in less than ten seconds after it was brought 
into action, which was generally advantageous as the cathode- 
fall tended to increase under action of the current. For 
this reason also the fall was obtained by a single deflexion of 
the electrometer-needle from its zero position—the latter 
being observed at the beginning and at the end of a series. 
Several independent tests were made, and though there was a 
marked variation in the magnitude of the fall under the 
different tests, yet they agreed with one another in placing the 
metals in the same series. Steel gave extremely erratic values; 
it also increased in fall so rapidly under action of the current 
that no definite value could be ascribed to it*. 
The results of three consecutive determinations of the 
cathode series are givenin Table II., for each of which the 
metals were newly polished. ‘They are arranged in the table 
according to their position in the contact-potential series f. 
It is to be seen that, with the exception of gold, the cathode- 
fall decreases in going from the platinum to the aluminium 
* For the same reason, tin could not be satisfactorily used as anode 
in either hydrogen or nitrogen. 
+ The potential series is taken from Jahn’s Grundriss d. Elektrochemie, 
p.4. The position of nickel is not given by Jahn; it is placed here as 
slightly less than bismuth, as obtained from Winkelmann’s Handb. d. 
Physik, 111. i. p. 119. 
