N. J. ALTHOUGH there have been many publications dealing with the determination of formaldehyde and higher aliphatic aldehydes, no reference has been found to a specific spectrophotometric method for determining formaldehyde.
Oxide film formation on a smooth platinum electrode in perchloric acid solution has been studied as a function of potential, current, time, and electrode history, using constant current and controlled potential techniques. Anodic film formation proceeds through two, single electron steps: a slow step followed by a fast (reversible) one. During film reduction the fast step occurs first, followed by the slow step. In the case of constant current reduction the slow step does not occur, and the film is exactly half-reduced. Complete reduction requires several hours at a controlled potential. Three electrode states are thus clearly defined: oxidized, half-reduced (active), and completely reduced or clean. A single kinetic equation quantitatively relates the current, potential, and time parameters, predicts the initial rate of opencircuit potential decay following film formation, and strongly suggests that the oxide is a chemisorbed film.
The use of chromotropic acid as a specific reagent for determining formaldehyde has been extended 80 that it can be applied in the presence of large concentrations of various organic compounds. In the presence of chromotropic acid, these interfering organic compounds are removed b y evaporation, whereas the formaklehyde is retained by the reagent. Subsequent addition of sulfuric acid develops the true purple color due to the formaldehyde present.
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