Pierre, a celebrated chemist, and member of the Institute of France, was born in 1725, at Chalons-sur-Marne. Showing a great inclination for study, he 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, and was employed for several years by the government in making analyses of the mineral waters of France.

On his return to Paris, he made analyses of different minerals 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 are used with striking effect in ornamental architecture; as may be seen in the columns of the Great Trianon at Versailles, in the interior of the church of St. Sulpice, and in other great buildings. These analyses are published in the Memoires presentés à l'Académie par divers Savans, commonly called Memoires des Savans Étrangers.

Bayen 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, who was present when the account of these experiments was read, was employed at that time in examining the metallic oxides; and soon after brought the subject into a clearer light, demonstrating the nature of oxygen, and the composition of the atmosphere.

Bayen 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. (W.A.C.)