Scientific memoirs : being experimental contributions to a knowledge of radiant energy / by John William Draper.

  • John William Draper
Date:
1878
Catalogue details

Licence: Public Domain Mark

Credit: Scientific memoirs : being experimental contributions to a knowledge of radiant energy / by John William Draper. Source: Wellcome Collection.

    418/488 (page 414)
    facts respecting the bleaching or clecolorization of clilo- rophyl by light. He used an ethereal solution of that substance: The first action of light is perceived in the mean red raj^s, and it attains a maximum incomparably gi-eater at that point than elsewhere. The next part affected is in the indigo, and accompanying it there is an action from + 10.5 to +36.0 of the same scale (Herschel's) beginning abruptly in Fraunhofer's blue. So striking is this whole result that some of my earlier spectra contained a ]3er- fectly neutral space, from —5.0 to +20.5, in which the chlorophyl was in no way changed, while the solar picture in the red was sharp and of a dazzling white. The maximum in the indigo was also bleached, pro- ducing a linear spectrum, as follows: in which the orange, yellow, and green rays are neutral. These, it will be remembered, are active in forming chlorophyl. Upon longer exposure, the subordinate action along the yellow, etc., occurs, but not until the other portions are perfectly bleached. In Sir J. Herschel's experiments there remained a salmon color after the discharge of the green. Tliis is not seen when chlorophyl is used, and is due to a color- ing matter in the leaf, soluble in water, but insoluble in ether. I have quoted these results in detail because they il- lustrate in a striking manner the law that vegetable col- ors are destroyed by rays complementary to tJiose that liave produced tliem, and furnish proof that rays of every refrangibility may be chemically active. At this point I abstain from adding other instances showing that chemical changes are brought about in every part of the spectrum. The list of cases here pre- sented might be indefinitely extended, if these did not