Forchhammer, Johan Georg

(b. Husum, Denmark, 26 July 1794; d. Copenhagen, Denmark, 14 December 1865)

geology, oceanography, chemistry.

Forchhammer was the son of Johan Ludolph Forchhammer, an educator, and Margrethe Elisabeth Wiggers. The elder Forchhammer was a teacher at the Citizens’ School in Husum and later became rector of a similar school at Tønder and manager of the teachers’ college.

Forchhammer’s early education was at the schools in Husum and Tønder. Following the death of his father in 1810, he became an apprentice in a pharmacy at Husum, where he stayed for five years. In 1815 he enrolled at the University of Kiel, studying physics, chemistry, pharmacy, mathematics, and mineralogy. He went to Copenhagen in 1818 and became involved in an investigation of the coal and iron layers of Bornholm, a rocky island in the Baltic. The investigating commission included Hans Oersted, at that time lecturing in physics and chemistry at the University of Copenhagen, and Councillor of Justice L. Esmarch. In 1819 he enrolled at the University of Copenhagen, and upon completion of his thesis “De mangano,” he received the doctorate in 1820.

Also in 1820 Forchhammer made a trip to England to further his understanding of geology, and there he became acquainted with such scientists as Prout, Davy, Dalton, Wollaston, Jameson, and Lyell. Together with Sir Walter C. Trevelyan he investigated the geology and coal formations of the Faeroe Islands; the resulting publication led to his becoming a member of the Royal Danish Academy of Sciences.

In 1821 Forchnammer became a lecturer in geology at the University of Copenhagen and also accepted employment at the Royal Copenhagen porcelain factory. Upon the opening of the Polytechnic Institute he became professor of chemistry and mineralogy and manager of one of its two chemical laboratories. He held this position until his death, and during the last fourteen years he was director of the institute. In 1831 Forchhammer was appointed professor of mineralogy and geology at the University of Copenhagen. From 1851 to his death he was secretary of the Royal Danish Academy of Sciences.

Forchhammer’s fundamental researches on the composition of seawater brought him international acclaim. He began this work in 1843, more as a geologist than as a chemist, to explain the phenomena that give rise to the deposits on the sea floor. His immediate goals were the factors governing the marine precipitation of calcium carbonate and the influence of volcanic activity on the oceans. He carried out analyses of over 160 samples collected for him over a twenty-year period by the Danish and British navies. He measured chlorine, sulfur, magnesium, calcium, and potassium gravimetrically with 100-pound samples, obtaining sodium from the differences.

The principal consequence of this work was the proposition that although seawaters exhibit marked regional differences in total salt content, the ratios of the major dissolved constituents to each other are almost invariable. With but slight modifications this concept is valid today. Forchhammer also posed in an elegant form the “geochemical balance problem” arising from the major sedimentary cycle: “Thus the quantity of the different elements in sea water is not proportional to the quantity of elements which river water pours into the sea, but inversely proportional to the facility with which the elements are made insoluble by general or organo-chemical action in the sea.” He reached this conclusion by noting that although calcium and silicon were often the principal constituents of river waters, they were less plentiful in the oceans. He correctly attributed the decrease in silicon to its incorporation into the skeletal material of the photosynthesizing diatoms but erroneously believed that calcium concentrations were regulated by carbonate-depositing animals.

Forchhammer’s pioneering efforts in Danish geology earned him the appellation “the father of Danish geology.” His fundamental work. Danmarksgeogno stiske Forhold (1835), was the first work on the structural geology of that country. This work and such other important investigations as those on the weathering of feldspars to clay minerals and the influences of biological materials upon the development of alums were always tinged with chemical insights. Forchhammer strengthened his arguments with chemical analyses. For example, he pointed out that trace quantities of heavy metals were present in almost all rocks as a result of their mobility in groundwaters circulating through fissures. His interest in soil chemistry extended to soil’s effect on the growth of plants. As a member of several commissions of the Royal Danish Academy he investigated the origins of the “kitchen middens” along the Danish shores together with zoologists and archaeologists.

BIBLIOGRAPHY

I. Original Works. Forchhammer published about 200 papers on geological and chemical subjects. Om Sövandets Bestanddele (Copenhagen, 1859) was translated into English as “On the Components of Sea Water” and published in Philosophical Transactions of the Royal Society, 155 (1865), 203–262. His treatise Danmarks geognostiske Forhold was published as a University of Copenhagen Report in 1835. He was also the author of several chemical textbooks.

II. Secondary Literature. See S. A. Andersen, in Dansk biografisk Leksikon, VII (1935); Axel Garboe, “Framyte til videnskab,” in Geologiens historie i Danmark, 2 vols. (1959–1961); Hans Pauly, “G. Forchhammer, en af geokemiens pionerer,” in Naturens verden (1967), pp. 24–32; 1 204–213, 224–246; and Johannes Steenstrup, “Forchhammer som menneske og personlighed,” in Meddelelser fra Dansk geologisk Forening, 8 (1935), 438–476.

Edward D. Goldberg