An autograph letter in French by the notable Dutch scientist and botanist Martinus van Marum, to the prolific Berlin chemist Johann Friedrich John, in which Van Marum declares John the winner of a competition of the Dutch Society of Sciences (Hollandsche Maatschappij der Wetenschappen) for his answer to the following question: "What is the origin of potash obtained from the ashes of plants; is it a product of the growth of vegetation and, hence, already present in those plants before burning them, or is it produced during the burning process?"
The competition was opened in 1812 and his thorough answer was published in 1917 in volume 8 of the Natuurkundige verhandelingen van de Hollandsche Maatschappij der Wetenschappen te Haarlem, pp. 39-160. The article would be published separately in German as Ueber die Ernährung der Pflanzen (1819).
Johann Friedrich John (1782-1847), a student of the outstanding chemist Martin Heinrich Klaproth, was invited to Moscow as Professor of Technical Chemistry at a projected Imperial Economic Institute in 1804. However, the plans for the Economic Institute did not move forward, and John had to return to Germany in 1806. Back home he started working as a private teacher and in 1811 he became Professor of Chemistry and Pharmacy at the University of Berlin.
Martinus van Marum (1750-1837) was secretary of the Dutch Society of Sciences and director of Teyler's Cabinet of Physical and Natural Curiosities and Library. "Although Van Marum made no great scientific discoveries, he greatly influenced the dissemination of knowledge in those fields of science that made great progress during his lifetime" (DSB).
In very good condition, with a small hole affecting two letters, some minor smudges, and a triangular piece of paper torn off on the address side from opening the letter. Cf. T. Sourkes "Devitalising the elements: Johann Friedrich John (1782-1847) and the liberation of phosphorus and potassium from a vital force" in: AMBIX XLVII, Part 1, March 2000; for John: Partington III, pp. 601-603; for Van Marum: DSB IX, pp. 151-153.