## Thermodynamische Begründung des photochemischen Äquivalentgesetzes

FIRST EDITION, EXTREMELY RARE OFFPRINT of Einstein’s paper on the first application of quantum theory to photochemistry; the Einstein-Stark law.

Einstein’s formulation of the photochemical equivalence law, a fundamental principle relating to chemical reactions induced by light, which states that for every quantum of radiation (photon) absorbed, one molecule of the affected substance reacts. Einstein’s formulation, founded on thermodynamics, marks the first application of quantum theory to photochemistry; it was one of his last significant contributions to quantum theory. The photochemical equivalence law is also known as the Stark-Einstein law: the German experimental physicist Johannes Stark had published his own derivation of the photochemical equivalence law in 1908, but at that time Stark did not agree with Einstein’s views on the corpuscular nature of radiation, and his argument was not based on quantum theory. Mehra and Rechenberg, *The Historical Development of Quantum Theory*, 1, pp. 103-104. Weil 46.

Offprint from: Annalen der Physik 37 (1912). 832-838pp. 221 x 145 mm. Original printed wrappers, edges a bit darkened, small splits in spine. Light toning but very good. Scarce in offprint form.

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