An important study of the properties of matter is the effect of chemical consti- tution upon the spectral absorption of a substance.The present contribution to this subject pertains to the infrared spectrum, extending to about 15/x.A description is given of the absorption spectra, to about 15m in the infrared, of the following plant pigments and derivatives: chlorophyll, carotin, xanthophyll, ethyl chlorophyllide, phytol, pheophytin, and copper pheophytin.The data were obtained by means of a mirror spectrometer, vacuum thermo- pile and iron-clad Thomson galvanometer described in previous publications.Changes in the absorption spectrum of carotin, accompanying oxidation, are described.In general, the results are similar to those observed on the highly colored ani- line dyes, in which there is an intense, wide absorption band in the short wave lengths, -and the infrared absorption spectrum is composed of numerous small absorption bands, in contrast with substances having a simpler chemical structure, in which the absorption bands are less numerous, more intense, and more sharply denned.
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Stair et al. (1933) studied this question.