of Edinburgh , Session 1868-69. 511 
rent during the oxidation of the kydrogenium may be shown in the 
following manner : — Use two palladium plates in the decomposing 
cell, with index to show the motion of the plate attached to each, 
as in the figure formerly given, and include in the circuit a com-* 
mutator and a fine spiral of platinum wire. During the occlu- 
sion of hydrogen the platinum spiral may be made of such a 
length as to remain dark, the motion of the index proving the 
absorption of hydrogen. If the direction of the current is now 
reversed the spiral of platinum becomes red hot, the index moving 
rapidly back to its original position, while the index of the other 
plate begins to move. The oxidation of the occluded hydrogen is 
the limit to the brightness of the platinum spiral, so that a reversal 
of the current produces a renewed brightness. By this arrange- 
ment we keep both indices moving along the scale, and the plati- 
num spiral alternately bright and dark. If the electro-motive force 
is really equal to a Bunsen’s cell, this arrangement must produce a 
current far more intense than any similar gas-battery, where oxygen 
and hydrogen are the reacting elements ; but as the resistance in the 
circuit might vary, several indirect experiments were made. When 
a palladium plate, saturated with hydrogen, was associated with a 
platinum plate in an acid solution of permanganic acid, and con- 
nected through a voltameter, the arrangement could decompose 
water. A similar result was obtained when a platinum plate coated 
with platinum-black saturated with oxygen was employed; but the 
action in this case was very slow, and sometimes did not succeed. 
A platinum plate covered with peroxide of lead was opposed to 
the hydrogenium; the combination decomposed water with facility. 
G-rove found two pairs of his gas-battery could effect a slow decom- 
position of water, and a single pair did as well if the oxygen was 
replaced by peroxide of lead. (The intensity of palladium and 
peroxide of lead combination must render it particularly well 
adapted to form secondary piles of great intensity, by substituting 
it instead of a lead plate in the arrangement devised by M. G-. 
Plante). The transformation of gaseous hydrogen into the oc- 
cluded state would seem to have little effect in reducing its total 
chemical energy, so that the occluded hydrogen must retain a 
relatively large proportion of the total gaseous energy in a 
potential form. If we compare the occlusion of gases to work 
3 x 
VOL. VI. 
