Conservation and Innovation : Helmholtz's Struggle with Energy ...

Volta's contact tensions in fact are not equivalent to a certain quantity of "force":
they do not produce an electrical imbalance but instead originate from an
electrical imbalance. For a correct interpretation of the processes it is necessary
to restrict the contact law to first class conductors (metals) and realise that the
second class conductors conduct only by means of an electrolytic process. Thus a
contact force can be interpreted in terms of attractive and repulsive forces of the
two metals which remove electrical charges of the contact area from one metal
to the other. Equilibrium is reached when an electrical particle in the passage
from one metal to the other does not acquire or lose living force, that is, when
the variation of living force from one metal to the other is compensated by an
identical variation of tension forces independently of the shape and dimension of
the contact surfaces and in agreement with the galvanic series of tensions.
Once more, conservation of force based on central forces gave a conceptual
explicative framework. But the case was different with the long analysis of
galvanic currents.
Conservation of force is applied to batteries not producing polarisation,
producing polarisation but not chemical decomposition and producing both. Here,
as enthusiastically remarked by Helm 207, conservation is applied in the nonmechanical
sense, as equivalence of numerical effects without a reinterpretation
in terms of living and tension forces. The first case, batteries without polarisation,
is the only one for which we have precise laws, experimentally corroborated.
Through the laws of Ohm, Lenz and Joule, Helmholtz gave the amount of heat
that must be generated in the circuit to have conservation of "energy". This heat
has to be equivalent to the chemical heat that would be developed without
electrical effects and the result is that the electromotive forces of the two metals
be proportional to the difference of the heat developed through their oxidation
and through their combination with acids.
The case of polarisation and of polarisation with chemical decomposition is
discussed in detail but only in a qualitative way, i.e. not only without the
application of the conceptual scheme, but even without quantitative indications,
for the lack of reliable empirical data 208.
Joule is quoted again, for his experiments intended to show the equivalence of
chemical and electrical heat 209. But again his results and methods are criticised
207 Helm Energetik P.44.
208 Helmholtz Erhaltung Pp.51-6
209 Joule Phil Mag XIX 1841 P.275; XX 1843 P.204; Helmholtz Erhaltung P.56.