SECTIONAL TRANSACTIONS.—B. 305 
These effects are not dependent on the presence of nitrogen, nor are they a manifes- 
tation of changes in the water-gas equilibrium. It can be assumed that with such 
a mixture as 2CO+0O,+4CO the dissociation of carbon dioxide is very slight 
(cf. W. A. Bone, Proc. Roy. Soc., 1925, 108 A, 408), but this mixture (when saturated 
with water-vapour at 22° C.) exhibits the glow very markedly. The mixture 
2CO+0,-++-5CO gives an even denser afterglow of approximately the same duration, 
namely, about thirteen times that of the flame period. With 2CO+0,+6CO the 
duration is nearly five times that of the flame period, and with 2CO+0,+7CO, 
nearly three times. That the glow is a concomitant of dissociation is thus the least 
likely of the several explanations which may be advanced. 
Comparable with the mixture 2CO+0,+4CO already referred to experiments 
have been made with a saturation of water-vapour at 45° C. The glow is still very 
marked, but it is strikingly less both in density and duration. This latter fact sug- 
gests a third explanation : that burning takes place in the mixture after the flame 
has passed through it. Certainly radiations that can affect a photographie plate 
occur after flame has travelled through the mixture. It is conceivable that these 
radiations are due to the subsequent burning of combustible gas which has escaped 
the passage of the flame. Experiments to test the possibility of such ‘ residual 
burning ’ occurring are in progress. This work is being carried out for the Safety in 
Mines Research Board, under the direction of Dr. R. V. Wheeler. 
Dr. R. V. WHEELER. 
Monday, August 31. 
6. Presidential Address by Prof. C. H. Duscu, F.R.S., on The 
Chemistry of Solids. (See page 30.) 
7. Mr. J. A. V. Butter.—The Seat of the Electromotive Force of the 
Galvanic Cell. 
The discovery of the production of an electric current by galvanic action gave rise 
to two distinct views of its origin, resulting in a controversy which was waged with 
considerable zeal for a century, without a decision being reached (cf. Sir Oliver Lodge’s 
comprehensive report, B.A. Report, 1884). On the one hand, physical theorists regarded 
as the chief factor a contact P.D. between the metals, identified with Volta’s contact 
force and an intrinsic property of the metals. On the other hand was the chemical 
view that the current had its origin in chemical effects at the electrodes. 
In the course of the nineteenth century, the chemical theory received convincing 
support from (1) the work of Davy and Faraday, which established the quantitative 
relation between quantity of electricity and chemical action ; (2) the discovery of the 
relation between the electrical energy produced and the energy of the reaction going 
on in the cell [Kelvin (1851) had postulated the equality of these. The exact thermo- 
dynamical relation was given later by Helmholtz and Gibbs]. (3) The Nernst conception 
of the process at metal electrodes which accounted for the effect of concentration. 
The chemical theory thus appeared to be established on all points. The Volta effect 
itself was explained as due to chemical action at the surface of the metals. For 
thirty years the metal junction was practically overlooked as an important con- 
tributor to the e.m.f. of the cell. 
Recent work on the thermionic and photoelectric properties of the metals (Richard- 
son, Compton and Millikan) has, however, conclusively demonstrated the existence of 
- large metal contact P.D’s. How are these to be reconciled with the chemical theory ? 
The author’s theory, based on statistical considerations, is outlined, which includes 
as different aspects of the whole truth (1) the existence of metal contact P.D’s 
between metals, approximately equal to the difference of their thermionic work 
functions, (2) the relation between e.m.f. and the energy of the chemical reaction 
expressed in the Gibbs-Helmholtz relation ; (3) the Nernst relation for the effect of 
concentration. 
1925 x 
