of Edinburgh, Session 1868-69. 
505 
cooled in an atmosphere of hydrogen, absorbed between six and 
seven hundred times its volume — increasing to the enormous 
occlusion of 982 volumes, when the metal used had been deposited 
by voltaic action. This occlusion of hydrogen, Graham has shown, 
can be easily effected at low temperatures by making palladium the 
negative electrode during the electrolysis of water. He has also 
shown that the metal, charged with hydrogen, has increased greatly 
in volume, and that its physical properties are entirely modified. 
So marked is the change in the physical, electrical, and magnetic 
properties of the combination, that the only class of compounds we 
can compare it with are the metallic alloys. In the occluded state 
the chemical intensity of hydrogen is increased, many reactions 
being effected by its agency beyond the power of the element in 
the free state. Graham, as a general result of his experiments, 
considers the occluded gas to exist in the form of a solid, with 
all the physical properties of a metal. During the course of an 
experimental exhibition of Graham’s discovery, I noted several 
phenomena associated with the occlusion of hydrogen by palladium, 
when it is made the negative electrode during the electrolysis of 
water; and as they illustrate, in a new form, the results already 
arrived at by the Master of the Mint, with his permission I am in- 
duced to bring them before the Society. 
If a palladium plate, used as the negative electrode during the 
decomposition of water, be arranged at right angles, instead of 
parallel to a similar platinum plate, the hydrogen in a short time 
is evolved at the edge of the palladium plate nearest to the platinum 
electrode — no trace of hydrogen coming from any other part of the 
plate. Gradually, as the saturation takes place, the hydrogen 
seems to travel slowly along the plate, and only after saturation is 
it freely evolved from the whole surface of the electrode. If we 
now reverse the current, so as to evolve oxygen at the palladium 
plate, immediately the nearest edge begins to evolve gas, the rest 
of the plate remaining tranquil, the evolution of oxygen moves 
along the plate in a gradual manner. This gradual transference 
depends on the time necessary to effect the occlusion, and on the 
relative intensity of the lines of force. 
When a palladium plate, charged with hydrogen, is brought in 
contact with a platinum electrode freely evolving oxygen, the 
