(b. Paris, France, 20 November 1685; d. Paris, 15 February 1766)
Hellot came of a well-connected, middle-class family and was destined for an ecclesiastical career. He turned to chemistry after perusing the papers of his grandfather, a physician; studied under E. F. Geoffroy; and then traveled to England, where he became acquainted with various fellows of the Royal Society. Having lost his fortune in the crash following the economic manipulations of John Law, he earned his living by editing the Gazette de France from 1718 to 1732. Hellot was elected adjoint chimiste of the Académie Royale des Sciences in 1735 and was promoted to pensionnaire chimiste supernuméraire in 1739 and pensionnaire chimiste in 1743. In 1740 he was elected a fellow of the Royal Society and in the same year was appointed inspector general of dyeing, a field in which he became an authority. He married in 1750, apparently desiring domestic comforts as he grew older. In 1751 he was appointed technical adviser to the Sèvres factory, where he is said to have introduced a number of technical improvements.
Hellot’s earliest researches were in pure chemistry: on the composition of ether, on metallic zinc and its compounds, on mineral acids, on phosphorus (whose method of preparation was apparently then unknown in France), and on Glauber’s salt. He soon showed remarkable ability as an analytical and industrial chemist, in part through service on various commissions of the Académie Royale des Sciences. In 1740 the Academy was asked to investigate the purity of certain samples of salt from various sources; Hellot did the major share of the careful analytical work involved. In 1746 he examined standard measures, an investigation arising from a query about the exact length of the ell. In 1763 he helped investigate firedamp in mines, a problem new to France.
But Hellot’s major contributions were to the chemistry and technical aspects of dyeing, and to mining and assaying. His L’art de la teinture des laines examines the techniques of fast dyeing materials of superior quality (“au grand teint”) and fugitive dyeing of cheap textiles (“au petit teint”). He advanced a mechanical explanation for the ability of the cloth to hold the dye: the particles of dye entered the pores of the cloth, and when these pores were closed, either by the inherently astringent properties of the dye or by those of the mordant, the particles of dye were then held fast. This theory had many adherents. The major importance of this book lay in the careful discussion of techniques which made it a standard work for the remainder of the century.
Hellot’s contributions to metallurgy are contained in his papers on zinc and on precious metals, but above all in his commentary on C. A. Schlütter’s work, also significant as one of the first French translations of a German chemical book, a genre very popular later.
Hellot was an original and effective practical and industrial chemist, one among the first generation of French scientists to concern themselves with technology.
I. Original Works. Hellot’s most important work is L’art de la teinture des laines et étoffes de laine au grand et au petit teint, avec une instruction sur les débouillis (Paris, 1750, 1786; Maastricht, 1772). In the English trans., The Art of Dying Wool... (London, 1789, 1901), the translator speaks of its having been “partly and poorly translated by a country Dyer, who knew but little French and no Chemistry,” but I have not been able to trace this earlier work, which may never have been published. There is also a German trans., Färbekunst (Altenburg, 1751, 1764, 1790).
Hellot’s remaining works were almost all in the form of essays published in the Histoire et mémoires de l’Académie royale des sciences, as follows: “Recherches sur la composition de l’éther” (1734); “Analyse chimique du zinc” (1734); “Conjectures sur la couleur rouge des vapeurs de l’esprit de nitre et de l’eau-forte” (1736); “Sur une nouvelle encre sympathetique à l’occasion de laquelle on donne quelques essais d’analyse des mines de bismuth, d’azur et d’arsenic, dont cette encre est la teinture” (1737); “Le phosphore de Kunckel et analyse de l’urine” (1737); “Sur le sel de Glauber” (1738), mainly on sulfuric acid; “Théorie chimique de la teinture des étoffes” (1740–1741); “Examen du sel de Pécais” (1740), written with Louis Lemery and C. J. Geoffroy; “Sur l’étalon de l’aune au bureau des marchands merciers de la ville de Paris” (1746) and “Sur l’exploitation des mines” (1756), both written with C. E. L. Camus; “Examen chimique de l’eau de la rivière d’Yvette” (1762), written with P. J. Macquer; “Mémoire sur les essais de matière d’or et d’argent” (1763), written with P. J. Macquer and Matthieu Tillet; and “Sur les vapeurs inflammables qui se trouvent dans les mines de charbon de terre de Briançon” (1763), written with H. L. Duhamel du Monceau and Étienne Mignot de Montigny.
Hellot also wrote the intro. to the trans. of a work on mining by C. A. Schlütter, published as Traité des essais des mines & métaux (Paris, 1750) and De la fonte des mines et des fonderies (Paris, 1753), with numerous additional comments.
II. Secondary Literature. The chief source for Hellot’s biography is the Éloge by Jean-Paul Grandjean de Fouchy, published in Histoire et mémoires de l’Académie royale des sciences for 1766. There is a short notice in F. Hoefer, Histoire de la chimie (Paris, 1866), II, 375–377; and a longer but confused account of his scientific contributions in J. R. Partington, History of Chemistry, III (London, 1962), 67–68, in large part based on the account in Thomas Thomson, History of Chemistry, 2nd ed., I (London, n.d.), ch. 8, 224–288. The best appraisal of his work is in Henry Guerlac, “Some French Antecedents of the Chemical Revolution,” in Chymia, 5 (1959), 73–112.
Marie Boas Hall