STAS, JEAN-SERVAIS

(b. Louvain, Belgium, 21 August 1813; d. Brussels, Belgium, 13 December 1891)

chemistry.

Stas was the son of a stovemaker of Louvain. As a boy he was taken to Paris by his elder brother Guillaume, a pupil of the sculptor François Rude, to pose for the statue Neapolitan Fisherboy Playing With a Tortoise, now at the Louvre. In 1832 Stas entered the medical faculty of the University of Louvain. After receiving the M.D. in 1835, he became assistant to his former professor of chemistry, Jean-Baptiste Van Mons, an expert in pomology who owned an apple nursery and experimented on fruit trees. When the nursery was displanted, Stas and Van Mons’s other assistant, L. G. De Koninck, were provided with a large supply of fresh roots of apple trees from which they isolated a crystalline glucoside that they named phlorizin. Stas conducted research on this substance in a small laboratory that he had equipped in the attic of his father’s house.

In 1837 Stas moved to Paris, to profit from the scientific milieu. As a collaborator of Dumas he performed a complete study of phlorizin, splitting it into phloretin and glucose. Stas published papers with Dumas on the composition of carbonic acid and on chemical types, and worked with him on the composition of water and on the action of potassium hydroxide on alcohols.

Stas’s career was markedly influenced by contemporary research on the composition of carbonic acid. Following Dalton’s hypothesis that the constant ratio combining weights of elementary substance is in the same ratio of their relative atomic weights, the determination of atomic weight had become an objective of prime importance to chemists.

In September 1840 Stas was appointed to the chair of chemistry at the Military School in Brussels. He began teaching in February 1841 under unfavorable conditions, for he lacked adequate facilities for research. During the next four years he contributed to the determination of the atomic weight of carbon. Proceeding by way of the combustion of carbon monoxide, he deduced the atomic weight as between 75 and 75.06 through comparing the weight of carbon dioxide formed by the reduction of a known weight of copper oxide under the action of carbon monoxide.

Following the publication in 1860 of his “Recherches sur les poids atomiques,” Liebig arranged financial help for Stas from the king of Bavaria, a gesture that inspired the Belgian government to grant him a subsidy of 6,000 francs, to cover three years’ expenses.

Like Dumas, Stas had been inclined to accept Prout’s hypothesis that atomic weights are wholenumber multiples of the atomic weight of hydrogen. In 1860 he published his main work, “Recherches sur les rapports réciproques des poids atomiques,” a study devoted to a number of elements (nitrogen, chlorine, sulfur, potassium, sodium, lead, and silver) that were considered by Dumas to support Prout’s hypothesis. In this work Stas demonstrated that the values of the atomic weights he had determined were neither multiples of unity, nor of one half, as Marignac believed, nor of one quarter, as Dumas maintained. This publication led Marignac to doubt the universality of the law of definite proportions. In three papers collectively entitled “Nouvelles recherches sur les lois des proportions chimiques, sur les poids atomiques et leurs rapports mutuels” (1865), Stas presented the results of an extensive series of experiments devoted to the new demonstration. By painstaking and accurate measurements he established that atomic weights were incommensurable, thereby disproving the facile conclusion that discrepancies with whole-number values were due merely to experimental errors. Prout’s hypothesis was thus discredited.

Stas determined atomic weights using indirect methods. To determine the atomic weight of nitrogen, for example, he measured (1) the amount of ammonium chloride required to precipitate the chloride of silver from a silver nitrate solution. The result was Ag : NH₄CI = 100 : 49.6; (2) the weight of potassium nitrate obtained by repeated evaporation of potassium chloride with nitric acid, and the weight of potassium chloride obtained from potassium nitrate by evaporation with hydrochloric acid; the result gave an atomic weight of 14.03; (3) the weight of silver nitrate obtained by the dissolution of silver in nitric acid and by evaporation; the result was that 100 Ag yielded 157.4952 AgNO₃ not fused, and 157.484 fused, which gives AgNO₃ = 169.99 (Ag = 107.94) ∴ N = 14.05. The mean result of these experiments was N = 14.09, which differs little from the currently accepted value, 14.008, achieved through the refinements introduced by recourse to physical methods.

Stas was also active in toxicology and published several papers on this subject in the early 1850’s. For a criminal case in which nicotine had been used he developed a method for detecting the poison in the victim’s body. It was later generalized to detect alkaloids in cases of poisoning.

Suffering from a herpetic disorder of the respiratory tract, Stas became professor emeritus in 1868. His pension covered only his living expenses. His modest inheritance was exhausted by the research expenses of the laboratory that he had equipped in his own house, where he accomplished the first part of his work on atomic weights.

In 1872 Stas resigned his post as commissioner of currency at the mint, to which he had been appointed in 1865. His simple way of life, his dedication to his work, his undaunted independence, exemplary tolerance, and commitment to the progress of higher education and research were made manifest in the deep influence he exerted in Belgium, which occasionally earned him disfavor in official circles.

BIBLIOGRAPHY

I . Original Works. Stas’s writings were collected in Oeuvres complètes, W. Spring and M. Depaire, eds., 3 vols. (Brussels. 1894).

II . Secondary Literature. On Stas and his work, see R. Delhez, “Jean-Servais Stas. 1813–1891,” in Florilège des sciences en Belgique pendant le XIXe siècle et le début du XXe (Brussels. 1968), 285–321; L. Errera, “Jean-Servais Stas,” in Revue de Belgique, 2nd ser., 4 (1892), 192–210; L. Henry, “Une page de I’histoire de la chimie générale en Belgique: Stas et la loi des poids,” in Bulletin de I’Académie royale de Belgique. Classe des sciences (1899), 815–848; J. W. Mallet, “Stas Memorial Lecture. Jean-Servais Stas and the Measurement of the Relative Masses of the Atom of the Chemical Elements,” in Journal of the Chemical Society, 63 (1893), 1–56; and J. R. Partington. A History of Chemistry, IV (London-New York, 1964). 876–878.

See also the following works by W. Spring: “Lecture sur la vie et les travaux de Stas,” in Bulletin de l’Académie royale de Belgique, Classe des sciences, 3rd ser., 21 (1878), 736–761; “Notice sur la vie et les travaux de Jean-Servais Stas,” in Annuaire de I’Académie royale de Belgique, 59 (1893), 2 17–376; and Académie Royale de Belgique, Biographie nationale, XXIII (Brussels, 1921 – 1924), cols. 654–684.

Also useful is Prout’s Hypothesis (Edinburgh, 1932), which contains papers by Prout, Stas, and Marignac.

Marcel Florkin