Chevreul (1815) "Lettre de M. Chevreul à MM. les rédacteurs des Annales de chimie" (Letter from Mr. Chevreul to the editors of the Annals of Chemistry), Annales de chimie, 94 : 73–79; in a footnote spanning pages 75–76, he mentions that he had found a substance that is responsible for the smell of butter.
Chevreul (1817) "Extrait d'une lettre de M. Chevreul à MM. les Rédacteurs du Journal de Pharmacie" (Extract of a letter from Mr. Chevreul to the editors of the Journal of Pharmacy), Journal de Pharmacie et des sciences accessoires, 3 : 79–81. On p. 81, he named butyric acid: "Ce principe, que j'ai appelé depuis acid butérique, … " (This principle [i.e., constituent], which I have since named "butyric acid", … )
E. Chevreul, Recherches chimiques sur les corps gras d'origine animale [Chemical researches on fatty substances of animal origin] (Paris, France: F.G. Levrault, 1823), pages 115–133.