176 Proceedings of Royal Society of Edinburgh. [sess. 
very significant fact (Mond, Ramsay, and Shields, Phil. Trans., 
cxci. 105), that fully charged palladium, no matter whether it 
exists as black, sponge, foil, wire or block metal, or whether it 
is charged by direct exposure to hydrogen gas (the proper condi- 
tions being observed), or charged electrolytically, has approxi- 
mately the same amount of hydrogen occluded in each case. 
This is well shown in the following table : — 
Atomic 
Ratio Pd:H. 
Yolumes of 
Hydrogen 
occluded. 
Palladium Black, 
1-42 
873 
j ) , , !• ) • • • 
V41 
881 
„ * .11, . . . 
1-40 
889 
„ „ III., • . . 
1-40 
889 
,, Sponge, 
1*46 
852 
„ Foil, 
1-47 
846 
Id • | 
f „ Wire, I. (Graham), . 
1-37 
912 
SC O pq 
f-i cs J 
1 „ ,, II. 
1-46 
846 
cS'g O i 
| „ „ HI- 
1-44 
859 
o >> 1 
t ,, Metal (Dewar), 
1-47 
847 
If the compound Pd 3 H 2 were formed, the theoretical value of 
the atomic ratio palladium: hydrogen would he P5. The ratio 
actually found varies between 1 *37 and 1 *47, which means that 
rather more than the theoretical quantity of hydrogen has been 
taken up. The excess, which is not large, as was the case with 
Troost and Hautefeuille’s hypothetical compound Pd 2 H, might be 
ascribed to a true occlusion, or perhaps a surface action after the 
formation of the compound Pd 3 H 2 . . 
A still greater excess, amounting to about ten per cent., may be 
forced into palladium, which is charged electrolytically, but this 
is immediately given off again on breaking the charging current. 
Increase of pressure up to four or five atmospheres does not 
influence the quantity of hydrogen occluded when the charged 
palladium is simply exposed to hydrogen gas. 
Up to this point, therefore, it still remained uncertain whether 
on the occlusion of hydrogen by palladium a solid solution or alloy 
was formed, or whether a definite chemical compound was pro- 
duced. The chief argument in favour of the formation of the 
