Jean-Antoine CHAPTAL (1756–1822) and Casimir de PUYMAURIN (1757–1841), chemists. Autograph letter signed by Chaptal and an autograph manuscript by Puymaurin; 1 page in-4, address (small tear repaired with loss of a few line endings), and 5 pages in-fol. Regarding the production of pastels in Albi. February 16, 1811. Chaptal thanks his dear Casimir for “the excellent pâté” he sent him: “My friend Raynouard draws inspiration from its enormous volume and finds it more substantial than any poem ever written or yet to be written”. He did not reply to him regarding the pastels, “because the timid prefect wrote to me that the minister had already taken offense at the fact that he had formed a commission without his spe[cial] authorization. Given these minor conflicts, I did not [wish] to press ahead.” He asks Puymaurin to pay for the shipment of the “pastel shells,” which he will reimburse him for. Notes and observations on the Alby facility for the extraction of indigo starch from pastel. Draft of a letter from Puymaurin to Chaptal, with marginal notes in another hand. In it, Puymaurin describes in detail the various operations for extracting indigo, following heat treatment in several vats and precise chemical processes… “The experiments to be conducted on the various plant species require a skilled individual, and Mr. Limousin Lamothe will be of the greatest assistance to me in these operations, for which even the smallest details must be recorded […]. In the batches intended for the experiments, it will be necessary to vary the methods of indigo production; we will test various methods of extracting it—whether by maceration in cold water, in hot water, or through fermentation—with the indigo leaves ground into a paste in a mill, half-dried, and the leaves lightly crushed by beating with sticks, etc.”… This is followed by the results of these experiments on the art of extracting indigo, the chemical composition of the starches, observations on yields, etc. Puymaurin indicates that he left a margin so that Chaptal could write down his “notes and observations.” Attached is a printed circular from Chaptal in his capacity as Minister of the Interior (3 Brumaire, Year XII).