Recherches thermo-chimique; (Extrait du Bulletin scientifique publié par l'Academie imperiale des Sciences de Saint-petersbourg, tome VII) (+) Recherches thermochimiques; (Suite du Mémoire imprimé dans les Annales...tome LXXV). (+) Recherches thermochimiques; Suite...). (3 Mémoirs).

Paris, Fortin, Masson et Cie, 1840 a. 1842. No wrappers. In "Annales de Chimie et de Physique", 2me Series - Tome 75 a. 3e Series - Tome 4.. With titlepage to Tome 75 and orig. printed wrappers to the issue (Septembre issue). Pp. 1-112 a. 1 engraved plate (entire issue offered). With titlepage to Tome 4. Pp. 129-256 (entire Fevrier issue) and pp. 257-384 (entire Mars issue). Hess' papers: pp. 80-103 (tome 75), pp. 211-229 (tome 4), pp. 290-316 (tome 4).

First appearance in France of Hess' two fundamental laws in thermodynamic 1: "the law of heat formation" (1840), anticipating a specific example of the "LAW OF THE CONSERVATION OF ENERGY", 2 years before Julius Robert Mayer elucidated the more general principle in 1842 - claiming that "the heat developed in chemical change is constant, whether the change occurs directly or indirectly in several stages"and 2: "the law of thermoneutrality" (1842), stating, that when neutral salts exchange acids and bases in solution, the heat of the reaction is zero. - These papers were published at the same time in France and in Russia.

Germain Henri Hess is noted today for two fundamental principles of thermochemistry: the law of constant summation of heat (known simply as Hess's law) and the law of thermoneutrality. These discoveries were remarkable in that they were postulated without any supporting theoretical framework and took place in a field of study almost totally neglected by his contemporaries. Hess's law is of immense practical importance and is used to this day to determine heats of reaction when their direct measurements are difficult or impossible. (Chemistry Encyclopedia).

"Numerous men, notably Lavoisier and Laplace had measured the heats evolved in various reactions, but thermochemistry received its first importent advance at the hands ofgermain Henri Hess, who showed that the heat evolved in a reaction is the same regardless of whether the reaction is carried out directly or in a number of steps. This generalization, known now as "Hess's Law", makes possible the calculation of heats for many reactions where direct measurement are impracticable."(Leicester & Klickstein, A Source Book..., p329.

"The thermochemical work of Hess was continued extensively in the second half of the nineteenth century through the studies of Thomsen and Berthelot. Both Berthelot’s principle of maximum work and the thermodynamic theories of affinity which came to prevail were clearly foreshadowed in the work of Hess.
In addition to his internationally known research in thermochemistry, Hess was very influential in the development of chemistry in Russia. His text Osnovania chistoy khimii (Fundamentals of Pure Chemistry) went through seven editions and did much to establish the chemical nomenclature of the Russian language. He was always interested in technological questions, and many of his students later contributed to Russia’s industrial development." (DSB).

Parkinson "Breakthroughs", 1840 C. - Leicester & Klickstein, A Source Book, p 329.

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