Vol. 7, 1921 
CHEMISTRY: D. P. SMITH 
29 
case of platinum, which has only a small occlusive capacity, and does not 
display the permanent increase, the supplementary conductance may be 
observed alone. 
Regarding the nature of this peculiar electrical conduction, three ex- 
planations seem thus far to offer : 
(1) The conduction is by a transient form of the occluded hydrogen, 
probably monatomic, and consists in a transport of electrical charges 
between points of different potential within the metal. 
(2) The conduction is by unstable hydrides, which are produced only 
under conditions of electrolysis which are equivalent to a high pressure of 
hydrogen, and which rapidly decompose when these conditions cease to 
obtain. (Newbery.) 2 
(3) The conduction, while not the result of chemical combination, is 
due to a temporary effect which the occluded hydrogen exerts upon the 
distribution or mobility of the electrons within the metal. 
Upon the second or third of these suppositions, there appears to be no 
reason to expect the character of the supplementary conduction to differ 
from that of metallic conduction in general ; but the first-named hypothesis 
leads to a different expectation. 
This first explanation, which has been suggested by the observation 
that the supplementary conduction and the volume of the alloy are directly 
related, may be stated somewhat more in detail as follows : 
It is supposed that within a hydrogen alloy there exist (a) molecular 
hydrogen, (b) atomic hydrogen, and (c) hydrogen combined with the metal 
to form solid solution ; and that these three forms are in mobile equilibrium 
in some such way as is indicated by the scheme 
2H + 2%MZ^H2M%HZ^LH 2 + 2xM. (1) 
Since the fact is well established that the formation of solid solutions 
between two metals brings about a great increase in the electrical resistance 
beyond the value which would result from simple mixture, it is natural 
to attribute the permanent increase of resistance in hydrogen alloys such 
as palladium-hydrogen to this combination; and if the supplementary 
conduction is attributed to the atomic hydrogen, it is evident that, upon 
the conception just outlined, this conduction must vary with the cathodic 
current density during electrolysis, as has been found to be the case, and 
must persist after the interruption of electrolysis until the equilibria of 
equation (1) have become established.* 
If the foregoing explanation be essentially correct, the conduction in 
question is that of a gas confined within the cavities of the metal. It is 
accordingly not to be expected that it will conform to Ohm's law, but 
rather that the resistance observed will depend upon the intensity of the 
current employed in its measurement, or in other words, upon the applied 
e. m. f . 
