A Manual Of Photography

THE COLOURING MATTER OE FLOWERS. 69 though less complete in degree Most commonly, vegetable colours, weakened by the action of alcohol, are speedily restore on the total evaporation of the ingredient But one remarkable instance of absolute dormancy induced by that agent ha curved to me in the case of Papayer orientale,?, flower of amu orange colour, bordering on scarlet the colouring matter ot which is not extractable otherwise than by alcohol, and then only in a state so completely masked as to impart no more than a faint yellowish or pinkish hue to paper, which it retains when thoroughly dry, and apparently during any length ot time, without perceptible increase of tint. 11 at any time, m^ever, a drop of weak acid be applied to paper prepared with this tincture, a vivid scarlet colour is immediately developed,thus demonstrating the continued though latent existence ot the colouring principle. On observing this it occui^d to^ to inouire whether, in its dormant state, that principle still retained it’“usceptibility of being acted on by light since the same powerful and delicate agent which had been sb cases as to constitute a general law, capable of disorganising and destroying vegetable colours actually developed, nug easily be presumed competent to destroy the capacity for assum; ing colour, in such organic matter as might Possess t under thh influence of their otherwise appropriate chemical stimuk. A strip of the paper was therefore exposed for an hour or to the spectrum, but without any sensible effect, à whole surface being equally reddened by an acid. As this experinien sufficiently indicated the action of light, if an), o ev’ I next placed a strip, partly covered, 111 a south-east indo, where it remained from June 19 to August 19, receiving the kw and scanty sunbeams which that interval of the deplorable su mer of 1841 afforded. When removed, the part exposed could barely be distinguished from the part shaded, as a trifle yellow er But on applying acid, the exposed and shaded portlons were^at once distinguished by the assumption of a vivid red in , and the former remaining unchanged. “A mezzotinto picture was now pressed on a glaze over another portion of the same paper, and abandone on the upper shelf of a green-house to whatever sun might occur from August 19 to October 19. The interval proved one of almost un- interrupted storm, rain, and darkness. On removal, no appear- 1,iwure^sed picture could be discerned, nor ance whatever of any impressen pitbull' was it even possible to tell the top of the picture from the bottom. It was then exposed in a glass jar to the fumes of muriatic acid, when, after a few Minutes, the development M the dormant picture commenced, and slowly proceeded, disclosing