1897 - 98 .] Dr John Shields on Palladium Hydrogen, 
179 
operate adversely. It has been found, however, that diffusion, and 
consequently equilibrium, does not always take place so readily as 
was anticipated, although the difficulties introduced in this way are 
not insuperable. 
Leaving out of account a few miscellaneous determinations of 
the electromotive force of charged palladium, the only literature 
bearing at all directly or indirectly on the subject is by C. G. Knott 
(Proc. Roy. Soe. Edin ., xii. 181) and by M. Thoma ( Gentralblatt f. 
Elektrotechnih , xi. 131), but the discussion of the results obtained 
by these observers is reserved for a later part of this paper. 
Several different forms of cell were constructed, the electrodes 
consisting of palladium wires attached to gold wires, palladium foil 
both new and foil which had been thoroughly ignited in the blow- 
pipe flame, palladium sponge shrunk on to platinum wires, palla- 
dium sponge and foil electro-deposited on gold foil, and palladium 
black existing as a layer on the surface of mercury electrodes. Of 
these forms of electrode one or two call for special mention. The 
palladium sponge shrunk on platinum (or gold wires) was prepared 
in the following way. The end of a hard glass tube about 8 mm. 
in diameter and 80 mm. long, was closed by means of a plaster of 
Paris plug. A wire was then pushed through the plug until it 
projected 10 or 12 mm. into the tube, and held in the axis of the 
tube until the plaster set. After drying, a quantity of palladium 
black was introduced and rammed tightly home. The open end 
was then attached to a Kipp’s apparatus supplying pure hydrogen, 
and a current of the gas was passed until all the oxygen had been 
removed and the palladium black charged with hydrogen. On 
now igniting the whole tube the hydrogen was driven off, and the 
palladium black, which decreases many times in bulk on passing 
into sponge, shrunk itself on to the wire and formed a rod of 
sponge. 
Although the electrodes, consisting of a layer of palladium black 
on the surface of mercury, which was connected by a platinum 
wire with the rest of the system, proved quite useless, they gave 
rise to other experiments which, although equally useless for the 
purpose, are worthy of being recorded. Such an electrode w’as 
charged electrolytically with hydrogen. A quantity of hydrogen 
which corresponded with what was required to remove all the 
