Peter, a celebrated chemist, member of the Institute of France, was born in 1725, at Chalons-sur-Marne. He showed a great inclination to study, and was sent by his parents to school at Troyes, where he went through a course of classical education with success. The bent of his disposition was to physical science. He went to Paris in 1749, and became the pupil and friend of an eminent druggist. In this situation he acquired a complete knowledge of the profession; and, before the age of thirty, he was appointed chief apothecary to the French army in Germany, in the Seven Years' War, a situation which he filled with industry, intelligence, and integrity.

After the conclusion of peace, he returned to Paris. The French government had employed Rouelle to name chemists for the purpose of analyzing the mineral waters which are found in different parts of France; and had allotted funds for this purpose. One of the chemists named was Bayen, and he employed himself ardently in these analyses for several years. His analysis of the waters of Barège and of Bagnères de Luchon are published; and besides the detail of accurate and well-contrived chemical processes, they contain matter interesting to the medical man, to the naturalist, and even to the general reader. He resided at the above-named baths, in the Pyrenees, whilst he was employed in analyzing the waters. The project of the French government was not carried farther than the analysis of these waters, so that the public employment of Bayen now ceased.

He returned to Paris, and made the analysis of different minerals which he had collected chiefly during his residence in the Alpine region of the Pyrenees. Amongst these is the marble of Campan, of which there are two varieties, the red and the green. They are brought from that country to Paris, where they make a distinguished figure in ornamental architecture; as may be seen in the columns of the palace of Great Trianon, in the interior of the church of St. Sulpice, and in other great buildings. These analyses are published in the Mémoires présentés à l'Académie par divers Savans, commonly called Mémoires des Savans Étrangers.

He made most accurate experiments on the oxides of mercury, to show that oxidation arises from the absorption of a portion of the atmospheric air, and that the existence of the phlogiston of Stahl could not be proved. Lavoisier was present when the account of these experiments was read, and was employed at the same time in examining the metallic oxides; and it was Lavoisier that brought the subject into a clearer light, and demonstrated the nature of oxygen, and the composition of the atmosphere.

Bayen published an analysis of tin and pewter. In consequence of the writings of some German chemists, fears had arisen amongst the public, that the use of these metals in culinary vessels was pernicious. Bayen showed that these fears were without any ground, if the pewter be of the legal standard, and be not fraudulently mixed with too great a portion of lead.

His mode of analyzing minerals required a long time; he exposed the mineral, without being reduced to powder, to the action of sulphuric acid at the temperature of the atmosphere; after this action had continued for a length of time, he got by lixiviation the sulphates formed by the combination of the acid, with the different component elements of the stone. He did not make use of the trituration of the stone to an impalpable powder, nor its fusion with caustic potash, which facilitate the subsequent action of acids, and which are used with so much advantage in the processes of modern chemists. The account he has published of his analysis will nevertheless be instructive to the chemical student, although the excellent and expeditious methods of Klaproth and Vauquelin are those that should be followed in practice.

He enjoyed good health till sixty, and died at the age of seventy-six, in the year 1801. He was a man of sound judgment, of strict integrity, and acquainted with several other branches of knowledge besides that which he particularly cultivated. There is a collection of his works, entitled Opuscules Chimiques, 1798, 2 vols. 8vo. (b. b.)