(b. Londorf, Germany, 23 December 1679; d. Halle, Germany, 25 October 1759)
Born in modest circumstances, Juncker received his primary education in Giessen. He was a student of philosophy at the University of Marburg in 1696 and then went to Halle, where he studied theology and followed a program in literature under the classical scholar Christopher Cellarius. Juncker taught in Halle from 1701 to 1707 and then left to study medicine in Erfurt, where he received his M.D. degree in 1717. In 1716 he had returned to Halle as physician to the Royal pedagogical Institute and Orphanage, beginning a distinguished career in that city which culminated in his appointment to the chair of medicine in 1729 and ultimately his selection as Prussian privy councillor. Juncker married three times.
The University of Halle, a Pietistic stronghold, possessed two of the outstanding chemical and medical theorists of the early eighteenth century, George Ernst Stahl and Friedrich Hoffmann. Juncker benefited from his close association with these brilliant colleagues and became one of Stahl’s most gifted and prominent disciples. When Stahl went to Berlin in 1716 Junker corresponded with him and published numerous dissertations and books that expounded and developed Stahlian ideas in chemistry and medicine. He reiterated Stahl’s admonition to keep these two disciplines distinct, arguing that chemical theory had little to offer medical practice at that time. His medical treatises censured both the iatrochemical and iatromathematical traditions and elaborated Stahl’s vitalist theories. Junker and another colleague in Halle, Michael Alberti, disseminated Stahlian vitalism throughout Europe and assisted in establishing an alternative in medical thought to the mechanical theories of Boerhaave.
Junker’s most important chemical text was the Conspectus chemiae theoretico-practicae in forma (1730), a systematic exposition of the ideas and experiments of Becher and Stahl. By providing a critical and coherent treatment of Stahl’s studies on chemical composition and reaction, the Conspectus offered a more intelligible version of Stahl’s work that gave it a greater audience. Junker stressed the necessity for grounding chemical theory in accurate and extensive experimental data and, after establishing the definition, aims, and utility of chemistry, applied the Becher-Stahl hierarchy of matter as the fundamental schema for chemical explanation. He adopted Stahl’s ideas on the nature of the elements, including phlogiston (which he emphasized was a material principle and not merely the property of burning) and, like Stahl, denied air a chemically active role, maintaining that it acted only as a physical instrument during reactions. Thus in combustion and calcination, air served to expedite the release of phlogiston from compounds, without itself entering into any chemical combination.
By effecting a clarification in Stahlian theory and methodology, Junker played a significant part in the development of his mentor’s ideas as a major force for reform in eighteenth-century chemistry. His concern with the broader implications of Stahl’s work, transcending other, more narrow approaches that focused on phlogiston, prefigured the orientation of important groups of chemists in Germany and France at mid-century.
I. Original Works. Many of Junker’s writings include Stahl’s name and method in their titles. Representative medical texts are Conspectus chirurgiae tam medicae methodo Stahliana conscriptae (Halle, 1721; 2nd ed., 1731); and Conspectus formularum medicarum ... ex praxi Stahliana postissimum, desumta (Halle, 1723; 2nd ed., 1730; 4th ed., 1753). Junker’s major chemical work is Conspectus chemiae theoretico-practicae in forma tabularum repraesentatus .... e dogmatibus Becheri et Stahlii potissimum explicantur (Halle, 1730; 2nd ed., 2 vols., 1742-1744), French trans. by J. F. Demachy, élémens de chymie, suivant les principes de Becker et de Stahl, 6 vols. (Paris, 1757). A complete list of Junker’s writings, including numerous dissertations on chemical and medical subjects, is given in Johnn George Meusel, Lexikon der vom Jahr 1750 bis 1800 Verstorbenen Teutschen Schriftsteller, VI (1806; repr. Hildesheim, 1967), 340-347.
II. Secondary Literature. Details concerning Juncker’s life appear in F. Hoefer, ed., Nouvelle biographie générale, XXVII (paris, 1858), 238-240; and Johnn C. Adelung Fortsetzung und Ergänzungen zu Christian G. Jöchers Allgemeinem Gelehrten-Lexicon II (Leipzig, 1787; repr. Hildesheim, 1960), 2347-2348. Brief assessments of Junker’s scientific work are J. F. Gmelin, Geschichte der Chemie seit dem Wiederaufleben der Wissenschaften bis an das Ende der achtzehnten Jahrhunderts. II (Göttingen, 1797-1798), 681; and James R. Partington, A History of Chemistry, II (London, 1961), 688-689