1902 Encyclopedia > Louis Jacques Thenard

Louis Jacques Thenard
French chemist

LOUIS JACQUES THENARD (1777-1857), was born on the 4th of May 1777, at Louptiere, near Nogent-sur-Seine, in Champagne. His father, though a poor man, sent him to the academy of Sens, where he received a liberal edu-cation. At the age of sixteen he' went to Paris to study pharmacy. He attended the lectures of Fourcroy and Vauquelin, and saw that the only way to learn chemistry was to work at it. Vauquelin, himself a poor man, ad-mitted a few students to his laboratory on payment of a fee of 20 francs a month. But this fee was prohibitory to the peasant's son ; the utmost that his father could send him just kept him alive in Paris. Thenard went to Vau-quelin and asked to be allowed to do any menial work for him, if only he would let him assist in his laboratory. One of Vauquelin's sisters had slipped into the room and heard part of the conversation; she said to her brother, " He is a good lad; you should keep him ; he will help you in the laboratory, and look after our pot au feu; your dandy assistants always let it boil." Thenard was engaged on these terms. Long afterwards he said that he looked upon the chemistry of the pot cm feu and the process of sim-mering as of very great importance: they had been the turning-point of his life. Thenard assisted Vauquelin in the laboratory and at his lectures, and, when by starving for a day or two he accumulated sous enough to pay for a seat in the gallery, used to go to the theatre to improve his pronunciation and rub off his rustic accent.
By and by Vauquelin gave him an opportunity of testing his powers as a lecturer. Having to go for some days to the country, he asked Thenard to take his place. For the first two or three lectures his attention was fixed on his work, and his eyes did not wander from the lecture table. On the fifth day he ventured to look round the room, when to his consternation he saw Fourcroy and

Vauquelin among the audience. They were so satisfied with what they had heard that they obtained for Thénard in 1797 an appointment as teacher of chemistry in a school, and in 1798 the post of répétiteur at the Ecole Polytechnique.
In 1804 Vauquelin resigned the professorship of chemistry at the College de France, and successfully used his influence to have Thénard appointed. In 1810 he succeeded Fourcroy both as professor of chemistry at the École Polytechnique and as member of the Academy. He was also appointed professor of chemistry in the faculty of the sciences. He was made a chevalier of the Legion of Honour in 1814, commander in 1837, and grand officer in 1842. In 1825 Charles X. gave him the title of baron; from 1827 to 1830 he represented the department of Yonne in the chamber of deputies. In 1832 Louis Philippe made him a peer of France. As vice-president of the conseil supérieure de l'instruction publique, he exercised a great influence on scientific education in France. He died 21st June 1857, and was buried at La Ferte, near Chalon-sur-Saône. In 1861 a statue was erected to him at Sens, and in 1865 the name of his native village was changed to La Louptière-Thénard. Thénard was tall and strongly built, his hair was thick and black, his eyes bright, and his manner active and prompt. He married, in 1810, Mile. Humblot, granddaughter of Conté. His wife and several of his children predeceased him. He was survived by his son Paul, who had assisted him in some of his later researches.
Thénard was above all things a teacher : as he himself said, the professor, the assistants, the laboratory, everything, must be sacrificed to the students. The history of his discovery of the peroxide of hydrogen well illustrates the predominance of the teacher in his character. He was lecturing on the formation of salts, and had told his students that a metal must be oxidized to a certain extent in order that it may combine with an acid to form a salt ; if the metal be combined with more than the proper quantity of oxygen, the excess of oxygen will be given off when the oxide is treated with an acid, and, as an illus-tration, he mentioned the action of acids on peroxide of barium. As he spoke his conscience smote him, for the experiment had not been made. Immediately after lecture he mixed peroxide of barium and nitric acid, keeping the temperature low by means of ice. He was surprised to see the peroxide dissolve without any evolution of gas. He left the mixture standing, and next day, before lecture, noticed small bubbles of gas rising from it. Pour-ing some of the liquid into a test-tube and warming it, he saw a large amount of gas escape, which he easily recog-nized as pure oxygen. At first he thought the acid had been oxidized, but he soon saw the true explanation of the phenomena, and discovered the peroxide of hydrogen. His lecture experiments were few, well-chosen, and accur-ately performed. If any failure occurred he would roundly scold his assistant, often apologizing for his vehemence when the short fit of anger was over. His lecture room, seated for 1000, was almost always crowded by eager and attentive students and visitors.
Like most great teachers, Thénard published a text-book, and perhaps we may say that by his Traité de Chimie Élémentaire, Théorique et Pratique (4 vols., Paris, 1813-16; 6th éd., 5 vols., 1833-36) he did even more to further the progress of the science than by his numerous and important original discoveries. His first original paper (1799) was on the compounds of arsenic and antimony with oxygen and sulphur. Careful analyses led him to conclusions as to the composition of the metallic oxides contra-dictory of some of Berthollet's theoretical views ; he also showed (1802) that Berthollet's "zoonic acid" was impure acetic acid. Berthollet, far from resenting these corrections from a younger man, took this opportunity of introducing himself, and invited Thénard to become a member of the "Société d'Arcueil," to the proceedings of which Thénard contributed important papers. Soon after his appointment as répétiteur at the École Polytechnique
Thénard made the acquaintance of Gay-Lussac, and formed with him a lifelong friendship. Their joint work, and its relation to the discoveries of Davy, have been fully recorded in the article GAY-LUSSAC. Of his separate investigations perhaps the most important is that on the compound ethers, begun in 1807. He showed that each acid gives its own ether, and that the acid and alcohol can be recovered by decomposing the ether by means of caustic alkali. His discovery of peroxide of hydrogen (1818) has already been described. His researches on sebacic acid (1802) and on bile (1807) also deserve special notice. The blue substance known as Thénard's blue (essentially aluminate of cobalt) was prepared by him in response to a demand by Chaptal for a cheap blue, as bright as ultramarine, and capable of standing the temperature of the porce-lain furnace.
Thénard's researches were chiefly published in the Annales de Chimie et de
Physique, in fche Mémoires de la Société d'Arcueil, and in the Comptes Rendus and
the Mémoires of the Academy of Sciences. (A. C. B.)

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