276 Prof. Oliver Lodge on the Seat of the 
present no experimental guidance beyond the barest qualita- 
tive one given by Mr. Brown, that copper-nickel reverses its 
sign when changed from air to hydrochloric acid, and that 
copper-iron is reversed in sulphuretted hydrogen. But satis- 
factory observation in these gases is difficult, because they not 
only tend to attack the plates, but they do attack them ; and 
so a film is formed and everything is rendered uncertain. 
Another complication results from the fact that, when metals 
are taken out of air and put into a foreign gas, they are 
already coated with a film of oxygen, and it is not clear in 
what way this will affect the action of the new gas. It may 
have to be replaced almost by substitution ; the affinity to be 
considered in chlorine, for instance, being something like 
M, Cl,—M, 0. Ina compound like HCl, the hydrogen also 
may have to be provided for, the resulting chemical strain 
being, for instance, M, Clh—M, Cl+ H,, O—2(H, Cl); but the 
consideration of the hydrogen affinities will not affect dijffer- 
ences, and therefore will leave comparisons with experiment 
unaffected. Taking the metals as clean, however, and without 
air-films, we must suppose the following series to be right. 
Energies of Combination of Metals with Chlorine ; and 
Calculated Volta Series in that Gas. 
Calculated 
Metal. Molecule. Authority. Ce Volta series, 
"| in Volts. 
Zu, Cl, Thomsen, 97210 21 
TENG sBonncdee : F. and 8. 100592 
. Andrews. 101316 
Lead Pb, Cl, Thomsen. 82770 18 
nse ho { y F. and 8. 89450 
| Fe,Cl, Thomsen. 82050 1:78 
Tron je.5.%-- | a F. and &. 99302 
BNC OL Ghee cect | Um eeaeeee No data. 
Cu,Cl, Thomsen, 51630 1:12 
Copper ...... a F. and S. 59048 
Fe Andrews. 60988 
Mercury ...... Hg,Cl, Thomsen. 63160 1:38 
Sil 2(Ag,Cl) ” 58760 1-28 
ee arcre: af F. and 8S. 69600 
2(H, Cl) Thomsen. 44000 96 
Hyd 2(H,Cl,aq.) " 78640 
Re sh gry 2(H,C1) F. and &, 47566 
2(H,Cl) Alvia. 48174 
2(K,Cl) Thomsen. 211220 4-62 
Potassium... a F. and §, 201920 
. Andrews. 208952 
Sodium: eee we: 2(Na,Cl) Thomsen. 195380 4°24 
This series will hold, as far as differences are concerned, for 
hydrochloric acid also ; because, whatever effect the hydrogen 
