THE THERMOCHEMICAL AFFINITY PRINCIPLE

THOMSEN, JULIUS.

Bidrag til et thermochemisk System [Contributions to a Thermochemical System]. (Særskilt aftrykt af det Kgl. Danske Videnskabernes Selskabs Skrifter, 5te Række, naturvidenskabelig og Matematisk Afdeling, 3die Bind.).

Kjöbenhavn (Copenhagen), 1852. 4to. Uncut and unopened in the original blue boards ("hollanderet"). A very fine, fresh, and clean copy - near mint, with only a bit of minor sunning to boards. 51 pp.

First edition, off-print, of the seminal paper that contains the first enunciation of the thermochemical affinity principle and the introduction of the term "varmetoning". The present paper represents Thomsen's main work as well as the "(to use Oswald's words) scientific creed of the chemist for the next half-century. It constituted the only method by which chemists could predict the course of chemical reactions, and Thomsen himself employed the theory in various ways to carry out calculations of this kind." (Brøndsted in: Meisen edt., Prominent Danish Scientists Through the Ages, p. 143).

This breakthrough work, which contains the first statement of a thermochemical nomenclatura and the first definition and presentation of the thermochemical affinity principle, inaugurated a several decades long period of thermochemical studies, during which Thomsen personally carried out more than 3,500 calorimetric measurements in a room kept at 18 degrees celcius. His fundamental thought was that the evolution of heat accompanying a chemical reaction ("varmetoning") is an exact expression of the chemical affinity of the reaction. Bethelot reached many of the same conclusions a bit later and advanced a theory that in essence was the same as Thomsen's. This led to heated discussions that continued for several years between the two scientists. Thomsen's principle is now usually known as the Thomsen-Berthelot-Principle. In 1883, the Davy Medal was awarded in duplicate, to "M. Marcellin Berthelot, Member of the Institute of France, and Foreign Member of the Royal Society, and Prof. Julius Thomsen, of Copenhagen", although Berthelot was obviously preceded by Thomsen.

"The importance of Thomsen's scientific work was rapidly recognized in both Denmark and abroad. In 1860 he was elected member of the Royal Danish Academy of Sciences and Letters. Nine years later he was nominated as professor of physical chemistry at the University of Leipzig, but he refused the offer. Many foreign scientists asked to work under his guidance, but he was afraid that the comparability of the results obtained would be endangered when more than one person performed such measurements and therefore refused all such requests. Thus no school was formed around him. Thomsen was a foreign member of various academies and honorary member of learned societies, and held honorary doctorates from several universities (but not in France, because of the conflict with Berthelot)." (D.S.B. XIII:359).

"Julius Thomsen's international reputation is due largely to his thermochemical studies. He began to work on thermochemical problems in 1850, and in 1852 he published in the "Videnskabernes Selskabs Skrifter" a paper entitled "Bidrag til et thermochemisk System" ["Contributions to a thermochemical System"], in which he outlined the scheme of his subsequent thorough investigations in this field. This paper contains the first enunciation of the thermochemical affinity principle, which states that chemical affinity, or the attraction between substances, can be measured by the heat evolved when they combine.
Ideas as to the nature and laws of chemical affinity were by no means lacking at this period, but the prevalent views were vague, hypothetical and mutually irreconcilable. The great importance of Julius Thomsen's principle when compared with earlier speculations lies not only in its fundamental theoretical ideas, which associate chemical and mechanical phenomena, but also in the fact that the conception of affinity is related to a measurable quantity, the "Varmetoning" - a term which Julius Thomsen introduced to include both evolution and absorption of heat - and thus is easily accessible to experimental investigation." (Brøndsted in: Meisen edt., Prominent Danish Scientists Through the Ages, p. 143).

Order-nr.: 41483