Pott, Johann Heinrich
POTT, JOHANN HEINRICH
(b. Halberstadt, Saxony, 1692; d. Berlin, Prussia, 29 March 1777)
Intended by his parents to study theology, Pott entered the University of Halle but soon turned to science, working under Friedrich Hoffmann and George Ernest Stahl. Both were professors of medicine who, in their teaching, separated chemistry from medical theory and practice. Pott was thus able to study chemistry as a subject in itself. He became professor of theoretical chemistry at the Collegium Medico-Chirurgicum in Berlin, where he succeeded Caspar Neumann in 1737 as professor of practical chemistry and director of the royal pharmacy. His career was characterized by great industry, wide reading, and fondness for personal controversy.
Pott’s principal contribution to chemistry was in the systematic examination of mineral substances. He extended knowledge of several metals, at a time when the traditional notion of a fixed number of metals was changing. Zinc, which had long been used as a constituent of brass, had only recently been isolated in sufficient quantity for detailed study. Pott characterized it as a distinct metal and prepared a number of its compounds, including zinc sulfate, showing that white vitriol was a compound of zinc and sulfuric acid. He described bismuth fully and added to knowledge of its compounds and those of borax, alkalies, and alkaline earths. Although useful and meritorious, this work did not raise Pott above the level of many competent contemporaries; it was the current interest in porcelain that brought out his true talent.
The introduction of porcelain to Europe in the seventeenth century stimulated attempts to imitate its hardness and translucence. The secret of its manufacture, relying on the use of a flux (alabaster, marble, or feldspar) with the otherwise infusible clay, was worked out chiefly by J. F. Böttger (1682-1719) at Meissen. The processes were kept so strictly secret by Böttger’s master, Frederick Augustus I of Saxony, that Meissen proved as impossible to duplicate as Chinese porcelain. Instructed by the king of Prussia to study the problem, Pott embarked on an extremely elaborate systematic investigation.
Pott reportedly made over 30,000 experiments on all manner of substances and mixtures subjected to heat in the furnace, and the results were published in his Lithogeognosia (1746). The elaborate tables of reactions in this work, quite apart from their relevance to manufacture, were a notable contribution to chemical analysis “in the dry way.“Mineral chemistry was just entering a period of rapid development made possible through analysis by the blowpipe and other related means. Moreover, Pott’s enormous repertoire of reactions was a model of comprehensiveness in chemical study and showed how relative reactivity could be found from planned, interrelated analysis. Although Pott did not speculate about affinity, his tables contributed greatly to that field of chemical theory.
Pott did not finally succeed in making porcelain, and that perhaps is the reason why Frederick the Great gave Marggraf (a younger man) preferment over Pott for the Berlin Academy. In 1754 Pott gave up chemical work, broke with the Berlin Academy, and burned his papers.
Pott held that phlogiston was the matter of fire but not of light. In his early practical writings he told his readers that he expected them to become familiar with current theories before reading his new work. His later writings were controversial and unproductive. By the time he reached old age, the tradition in which he had been brought up was about to be swept away by the systematic, experimental approach to chemistry that he had helped to create.
I. Original Works. Pott’s main work is Lithogeognosia; Chymische Untersuchungen (Potsdam, 1746; Berlin, 1757), also trans. into French as Lithogéognosie (Paris, 1753). Other of his writings are collected in Exercitationes chymicae (Berlin, 1738), French trans., with additions, by J. F. Demachy (Paris, 1759); and Observationum et animadversionum chymicarum, 2 vols. (Berlin, 1739-1741).
II. Secondary Literature. See J. H. S. Formey, Histoire de l’ Académic royale des sciences et belles letters de Berlin (Berlin, 1777), 55; J. R. Partington, History of Chemistry, II (London, 1961), 717-722, with bibliography and extensive notes; and J. R. Spielmann, Instituts de chymic, II (Paris, 1770), 409-417, with bibliography.