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Karl Friedrich Mohr

Karl Friedrich Mohr (November 4, 1806 - September 28, 1879) was a German pharmacist famous for his early statement of the principle of the conservation of energy. Ammonium iron(II) sulfate, (NH₄)₂Fe(SO₄)₂.6H₂O, is also called Mohr's salt, after him.

Being a delicate child and the son of a well-to-do druggist in Koblenz, he received much of his early education at home, in great part in his father's laboratory. To this may be traced much of the skill he showed in devising instruments and methods of analysis. At the age of twenty-one he began to study chemistry under Leopold Gmelin, and, after five years in Heidelberg, Berlin and Bonn, he returned with the degree of Ph.D. to join his father's establishment.

On the death of his father in 1840 he succeeded to the business, retiring from it for scientific leisure in 1857. Serious pecuniary losses led him at the age of fifty-seven to become a privatdozent in Bonn, where in 1867 he was appointed, by the direct influence of the emperor, extraordinary professor of pharmacy.

Mohr was the leading scientific pharmacist of his time in Germany, and he was the author of many improvements in analytical processes. His methods of volumetric analysis were expounded in his Lehrbuch der chemisch-analytischen Titrir-methode (1855), which won the special commendation of Liebig and has run through many editions. His Geschichie der Erde, eine Geologic auf neuer Grundlage (1866), also obtained a wide circulation.

In a paper Über die Natur der Wärme (1837), he gave one of the earliest general statements of the doctrine of the conservation of energy in the words:

"besides the 54 known chemical elements there is in the physical world one agent only, and this is called Kraft (energy). It may appear, according to circumstances, as motion, chemical affinity, cohesion, electricity, light and magnetism; and from any one of these forms it can be transformed into any of the others."

• Mohr, K.F. (1837) "Ansichten über die Natur der Wärme." Ann. der Pharm., 24, pp. 141–147.
• - (1876) (trans. P. G. Tait) "Views of the nature of heat." Philosophical Magazine 2 110-14.

This article incorporates text from the Encyclopædia Britannica Eleventh Edition, a publication now in the public domain.