Theoretical chemistry from the standpoint of Avogadro's rule & thermodynamics / [Walther Nernst].
- Walther Nernst
- Date:
- 1911
Licence: In copyright
Credit: Theoretical chemistry from the standpoint of Avogadro's rule & thermodynamics / [Walther Nernst]. Source: Wellcome Collection.
801/840 page 777
![tion and description of the particular phenomena belonging here, and therefore we will only refer to the very complete bibliography prepared by Eder.1 But it should be emphasised that gases (as, e.g., the explosive mixture of hydrogen and chlorine), liquids (as, e.g., chlorine water, which gives up oxygen, under the influence of light), and solids (as, e.g., white phosphorus, which changes to the red modification in the light; or cinnabar, which turns black), all respond to the ether vibrations. Also the photo-chemical process may consist both in the production of a compound, as is the case with hydrochloric acid gas, and in the decomposition of a compound, as is seen in the decomposition of hydrogen phosphide, with the separation of phosphorus. Trautz2 has recently shown that light sometimes acts as an anticatalyst, and that in the same reaction (e.g. oxidation of pyro- gallol by oxygen) one kind of light (e.g. violet light) accelerates, and another (e.g. red light) delays the reaction. The sensitiveness to light of organic compounds has been systematically worked out by Ciamician and his colleagues. In a review of the whole material (Bull, de la Soc. Ghem. iii., iv., No. 15, p. 1) he considers the influence of light on oxidations and reductions. A whole series of bodies with alkoxyl groups react on substances containing carbonyl, the alcohol group being oxidised by the carbonyl oxygen. For instance, ethyl alcohol reacts on quinone to give aldehyde and hydroquinone besides some quin- hydrone. Especially interesting are the mutual internal oxidations and reductions of bodies containing nitrogen: e.g. o-nitrobenzaldehyde goes over to o-nitrosobenzoic acid. Other classes of reactions which are especially influenced by light are enumerated by Ciamician as follows: autoxidations, polymerisations, and condensations, the change from the fumaric to the maleic type, and hydrolysis (e.g. splitting up of cyclic ketones). In this way many reactions can be carried out which take place with difficulty, or not at all, in the dark. Organic photo-reactions are catalysed to a large extent by uranium salts. (Seekamp, Ann. d. Ghem. 122. 113 [1862] and 133. 253 [1865].) Although, on the one hand, this kind of light action in photo- chemical processes varies greatly according to the nature of the system illuminated, in contrast to ordinary absorption which always develops heat, yet like ordinary absorption it is highly dependent upon the wave-length of the light vised. Thus we know photo- chemical reactions which are mainly caused by ultra-violet rays, or by the visible rays, or by the ultra-red rays of the spectrum, respectively; and in all cases the intensity of the plioto-chemical action depends in the highest degree upon the wave-length of light, 1 Handbuch der Photochemie, Halle, 1906 ; Fehling’s Ifandwdrterbuch, under Chemische Wirkungen des Lichtes. See further M. Itoloff, Zeitschr. phys. C/iein. 26.337(1898). * Physik. Zeitschr. 7. 899 (1906).](https://iiif.wellcomecollection.org/image/b28047850_0801.jp2/full/800%2C/0/default.jpg)
