1 9 2 D O C . 2 3 1 W A R B U R G A S R E S E A R C H E R in this case substantially (e.g., around 40°) smaller than . Entirely different from polarizable electrodes, for ex., mercury-dilute sulfuric acid. In this case the phase delay of the polarization tension against the current at a high frequency of the al- ternating current is just a little smaller than the electrode thus behaves similarly to a high-capacity condenser. Warburg shows that this case can be interpreted as that products of electrolysis, e.g., hydrogen, are periodically electrolytically dis- charged from the (platinum) electrode and dissolved, where the difference in po- tential between electrode-electrolyte depends linearly to first approximation on the discharged amount. Without diffusion of this discharge (e.g., hydrogen) into the so- lution and into the interior of the electrode, the phase difference between current and tension would be but this diffusion reduces the phase difference. These pro- cesses are analyzed by Warburg in the second of the mentioned papers. The numerous subtle analyses on the chemical effects of silent electric discharge will have to be acknowledged by others who can judge the mastery of experimental precision work better than I, likewise the precision analyses Warburg conducted together with physicists from the Physikalisch-Technische Reichsanstalt on Planck’s radiation formula. Whoever wishes to gain insight into Warburg’s gener- ously inventive experimental skill, critical foresight, and indefatigable working energy will have to study the original contributions. But we must still give tribute to the photochemical papers of the last century, which—it is permissible to say without exaggeration—provided the initial basis for quantitative photochemistry. From gas reactions he showed in an entirely impeccable way—first in 1906 from gaseous hydrogen bromide—that the primary process constitutes the absorption by a molecule of the energy quantum hv of the effective radiation. This primary pro- cess of absorption has on its own nothing to do with the subsequent chemical reac- tions, to which it merely supplies the energy. The molecule loaded with one absorbed quantum now has special reactive options. It can either disintegrate spon- taneously (at sufficient magnitude of the quantum energy), whereupon the fission products continue to react with other molecules or else the molecule, equipped with one absorbed quantum, can react chemically in a certain way with other mol- ecules. Only in the case where these chemical reactions are unambiguously linked with quantum absorption will the number of converted moles per quantum be the- oretically predictable, e.g., in the case of HBr, where one molecule H2 and one mol- ecule Br2 is formed per quantum of absorbed radiation. The lateness of this π 2 -- - π 2 -- - π 2 -- -
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