Johan Georg Forchhammer was a German-born Danish chemist and geologist. He was a professor of mineralogy and geology at the University of Copenhagen.
Background
Johan Forchhammer was born at Husum, Schleswig, on the 24th of July 1794. He 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.
Education
Johan entered the University in Kiel, where he studied physics, chemistry, and pharmaceutics, as well as interested in mathematics and mineralogy. In 1819 he enrolled at the University of Copenhagen, and upon completion of his thesis “De mangano,” he received the doctorate in 1820.
Johan 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 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.
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 a 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 a director of the institute. In 1831 Forchhammer was appointed a 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. 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 fundamental work, Danmarks geognostiske Forhold, was the first work on the structural geology of Denmark. 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. He also investigated the origins of the “kitchen middens” along the Danish shores together with zoologists and archaeologists.