278 Prof. Oliver Lodge on the Seat of the 
But it will be observed that this is nothing like the order 
to be expected in sulphuretted hydrogen ; for it is popularly 
known that copper is more easily sulphurized in this gas than 
iron. Now assuming that the metal had been covered with 
an air-film, and that the oxygen of this has to be replaced by 
sulphur, the chemical tendency, instead of being M,§S, is 
something more like M, S—M, O, or possibly M, S—M, O+ 
H,, O—H,, 8; and either of these will give a quite different 
order. Data are given on p. 624 of Naumann’s G'melin-Kraut, 
vol. i., for the neutralization-heats of various bases by H, 8, 
such as CuO+ H, 8, &e. These are something like what we 
want, and from them we reckon the following :— 
Hypothetical Volta Series, in Sulphur or Sulphuretted Hy- 
drogen, of Metallic Oxides, and possibly of Air-coated 
Metals. 
Heat of reaction, 
Metal. MO-++H,S—MS8+H,0. Volts 
Silverson Mecesecses 55800 1:20 
Mieneuinya =e. 41700 1:04 
Copper kaasent.: 31600 68 
CAC owes s auras 26600 57 
DANO? Soe Pe 19200 ‘Al 
PPOs eee en hoes 14600 Ol 
Sodaumalc.:ee- 42 7700 16 
The series so obtained gives copper and iron in their proper 
order ; but it is scarcely likely to be really correct, because it 
assumes that the oxides of the metals are exposed to the gas 
rather than the metals themselves. It is quite possible that 
it is not very incorrect for tarnished metals, 7. ¢. metals coated 
with a film of oxide ; but for ordinarily clean metals, coated, 
not with a film of oxide, but with a film of oxygen, it is 
nothing but a rough approximation, given because we have 
no better data. 
It is to be noted that, as the film of oxygen diffuses away, 
the Volta-effect depending on it must diminish ; until at length 
the active affinity causing the chemical strain is nothing more 
than M,S or perhaps M,S—H,,8. A gradual falling off 
and ultimate even reversal of sign was observed by Mr. Brown 
in both HCl and H,8. In so far as actual chemical action 
occurs and a film of chloride or sulphide forms, so far of 
course also will the effect diminish ; because it depends essen- 
tially on the unsatisfied chemical strain, not on the accom- 
plished chemical action. 
