César DESPRETZ (1791-1863), chemist and physicist, President of the Académie des Sciences. 6 autograph letters signed to the chemist Edmond Frémy (1814-1894), professor at the Muséum. 6 pp. in-8. 1859-1861 and n.d. Some addresses on the back, one stamped. Nice correspondence between these two chemists against a background of competition between scientists, in which he fiercely defends his work (discoverer of mustard gas, he did important research in thermodynamics and was the first to study the transformation of carbon into diamond). "Since several chemists claim that chemistry has done what I have just done with so much trouble, please be so kind as to show me a work that resembles mine in some respects". "Would you tell me if there are any experiments on this question: a mixture of equal atomic weights, or in another ratio of two metals, e.g. copper and lead, is precipitated with hydrogen sulphide. The precipitates are separated into four. Do we know the composition of these products? I was going to do some experiments with this in mind, I need them for my work, but as I already have to do a large number of them, I would not do them if they were already done by a chemist [...]". "I beg you to accept a copy of my old chemistry. It is impossible for me to find a clean, new copy. It has not been in the bookshop for a long time [...]". "Please send me a copy of Mr Pelouze's paper on Prout's law. I am not stealing anything from your friend. I am only quoting it, I will show you all of it, the memoir on metallic acids [...]", etc.