‎"HESS, (GERMAIN HENRY). - ""THE LAW OF HEAT FORMATION""‎
‎Recherches sur les quantités de chaleur dégagées dans les combinaisons chimiques. (Lettre à M. Arago).‎

‎Paris, Fortin, Masson et Cie, 1840. 8vo. Contemp. hcalf. Spine gilt and with gilt lettering. Some scratches to spine. In: ""Annales de Chimie et de Physique"", 2e series, tome 74. 448 pp., 1 folded plate. Hess' paper: pp. 325-335. Stamps on verso of titlepage. Internally clean.‎

Reference : 48910

‎First edition of Hess's most famous paper, in which he outlined his law on thermochemistry. His principle, a progenitor for the first law of thermodynamics, came to be called Hess's law. It states that in a series of chemical reactions, the total energy gained or lost depends only on the initial and final states, regardless of the number or path of the steps. This is also known as the law of constant heat summation. Hess described here his newly discovered law, known as Hess's Law, in form of a letter to Arago. (The letter was also published in Comptes Rendus in a slightly modified form). ""Here thermochemistry received its first importent advance at the hands of Germain 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..."" (Leicester & Klickstein ""A Source Book in Chemistry"", pp. 329-332). This paper preceded the larger papers also published in ""Annales de Chimie et de Physique"" and the original (and larger) paper in ""Bulletin scientifique, Academie impériale des Sciences (St. Petersbourg, 1840)"". The volume contains also papers by Laurent, Biot, Mulder, Melloni etc.Parkinson ""Breakthroughs"" 1840 C.‎