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

generate a determined equivalent of heat, however complicated the transition
from one force to the other" 56. Helmholtz asserted that the empirical evidence
was not very large but still he wanted to offer specific theoretical applications of
the principle to the heat produced through mechanical, chemical, electrolytic and
electrostatic forces. The case of animal heat was now only the last of five
applications of a principle that was becoming more and more general.
A great difficulty immediately appeared: the most important balance, the
one between heat and work, could not be written for the lack of a mechanical
equivalent of heat; in fact the values offered by the theories of Carnot-Clapeyron
and Holtzmann could not be accepted, being based on the caloric model and only
referred to the propagation and not to the production of heat 57. Helmholtz, despite
having clearly focussed the problem, lacks experimental data. In October 1846 he
still did not know of Mayer's nor of Joule's work: "no experiment can be taken in
account for the mechanical forces" 58. Thus all the other balances were written as
equivalences based on heat units and not on work units. In the "Bericht" heat and
not work was the unity of measurement common to all the natural phenomena
considered, not a minor difference with the subsequent Erhaltung.
In the analysis of chemical transformations Hess' law of the constancy of
the production of heat, whichever the intermediate stages of the reaction, was
acknowledged. Here appeared the first instance of the identification of latent heat
with the thermal equivalent that was to play a role in the subsequent discussion of
animal heat.
For the electrolytic currents the heat developed in the circuit must be
equivalent to the electrochemical transformations in the galvanic chain (battery),
independently of their order. The heat in the circuit could be calculated through
Georg Simon Ohm's and Emily Christianovic Lenz's laws (Joule was not
mentioned):
frictional electricity, where a release of latent heat is inconceivable". Helmholtz: W A 1 Pp.6-
7.
56 Helmholtz W A 1 P.7
57 It is interesting to remark that instead in the Erhaltung these data were utilised,
that Clausius criticised this "improper" use, that Helmholtz accepted the criticisms, that
Truesdell denies the validity of these criticisms. See below.
58 Helmholtz WA 1 P.7.