(b. Châlons-sur-Marne, France, 7 February 1725; d. Paris, France, 15 February 1798)
Bayen received his early education at the Collège de Troyes. After deciding on a career in pharmacy, he was placed with the pharmacist Faciot in Rheims. In 1749 he went to Paris and studied under P. de Chamousset and G. F. Rouelle.
With G. F. Venel, Bayen was commissioned by the government in 1753 to analyze all the mineral waters of France, but this work had to be suspended when he was sent as chief pharmacist on an army expedition in 1755. Later, after continuing the analyses alone for many years, he finally had to abandon the work for lack of funds. From 1763 to 1793 Bayen was apothicaire-major des camps et armées du roi, and he became pharmacien inspecteur to the Conseil de Santé in the latter year. He was never elected to the Academy but became a member of the Institut de France when it was founded in 1795.
Bayen’s first publication was an analysis of the mineral waters of Bagnères-de-Luchon (1765), a long and detailed work published only incompletely in his Opuscules. However, his most important contribution to chemistry was a series of four memoirs on the precipitates of mercury (1774–1775). His observations led him to doubt the phlogiston theory, for he noticed that when red precipitate (mercuric oxide) was heated alone (in which case, there was no reducing agent to supply phlogiston to it), it was reduced to mercury and a large quantity of an elastic fluid was produced. He made careful quantitative observations of all that took place and concluded that when mercury was calcined, it did not lose phlogiston but combined intimately with the elastic fluid, and that this addition of elastic fluid to the mercury was responsible for its increase in weight. He failed to identify the elastic fluid (oxygen), however, and did not even apply the simple test of plunging a lighted taper into it.
Bayen helped to make known the work of Jean Rey, the seventeenth-century Périgord doctor whose theory of calcination was very similar to his own.
In 1781, Bayen produced a report, commissioned by the Paris College of Pharmacy, on the alleged presence of arsenic in tin. Henckel and Marggraf had reported that commercial tin contained arsenic, which would have made its use in kitchen equipment dangerous. Bayen concluded that, at the most, the tin contained only a trace of arsenic.
In addition to these researches, Bayen published analyses of minerals (1776, 1778, 1785, 1798). Some of his work, however, cannot be traced, because he burned all his manuscripts during the Terror.
Bayen was a thorough and careful worker, and often spent years examining a material, seeking the least destructive method of analysis in an attempt to imitate nature and preserve the constituents intact. That he was forty when he published his first memoir was doubtless a consequence of this reluctance to commit himself to paper before he had conducted the most exhaustive research.
I. Original Works. A detailed bibliography of Bayen’s writings is in A. Balland, ed., Travaux scientifiques despharmaciens militaires français (Paris, 1882), pp. 6–8. His works were collected in Opuscules chimiques de Pierre Bayen, P. Malatret, ed., 2 vols. (Paris, 1798), in which the memoir “Analyse des eaux de Bagnères-de-Luchon, par ordre du ministre de la guerre” is incomplete. A complete version of this memoir is in Richard, Recueil d’observaions de médecine des hôpitaux miltaires, II (Paris, 1772), 633–778; it was originally published, complete, in an octavo volume (Paris, 1765).
II. Secondary Literature. Works on Bayen are A. Balland, “En mémoire de Bayen,” in Journal de pharmacie et chimie, 8th ser., 1 (1925), 83–94; P. A. Cap, “Étude biographique sur Pierre Bayen,” ibid., 4th ser., 1 (Jan. 1865); P. Lassus, “Notice historique sur Bayen,” in Annales de chimie, 26 (an VI ), 278–288, also published as “Notice sur la vie et les ouvrages du Cen Bayen.” in Mémories de l’Institut national des sciences mathématiques et physiques, 2 (fructidor, an VII ), hist., 144–152; A. A. Parmentier, “Eloge de Pierre Bayen,” in Bayen’s Opuscules, I. xxxiii-lxxiv; see also “Discours préliminaire,” ibid., pp. iii-xxxii, which contains sections of another éloge, not published elsewhere, in which some of Bayen’s ideas are discussed; M. B. Reber, “Une lettre inédite de Pierre Bayen, suivie de quelques observations,” in Bulletin de la Société française d’histoire de la médecine, 9 (1910), 50–63; and A. F. Silvestre, “Notice sur le Citoyen Bayen,” in Rapports généraux des travaux de la Société philomathique de Paris, I (1793), 233–240.