176 HISTORY OF PHOTOGRAPHY. 



vigor. Ill like manner allialies restore the color, converting it at the same time 

 into green. 



Papaver orientule. — The cliemical babitndes of the sulphurous acid render it 

 highly probable that its action in including a dormant state of the colorific 

 principle consists in a partial deoxidizement, unaccompanied, however, with 

 disorganization of its molecules. And this view is corroborated by the similar 

 action of alcohol already spoken of — similar, that is, in kind, though less com- 

 plete in degree. Most commonly vegetable colors weakened by the action of 

 alcohol are speedily restored on the total evaporation of the ingredient. But 

 one remarkable instance of absolute dormancy induced Ity that agent has 

 occurred to me in the case of Papaver oriciifale. a tlower of a vivid orange 

 color, bordering on scarlet, the coloring matter of 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 i)aper, which it retains 

 when thoroughly dry, and apparently during any length of time, without per- 

 ceptible increase of- tint. If at any time, however, a drop of weak acid be 

 applied to paper ])repared with this tincture a vivid scarlet color is immediately 

 developed, thus demonstrating the continued though latent existence of the 

 coloring principle. On observing this, it occurred to me to inquire whether, in 

 its dormant state, that principle still retained its susceptibility of being acted 

 on by light, since the same powerful and delicate agent which had been shown, 

 in so many cases as to constitute a general law, capable of disorganizing and 

 destroying vegetable colors actually developed might easily be presumed com- 

 petent to destroy the capacity for assuming color, in such organic matter as 

 might possess it, under the influence of their otherwise appropriate chemical 

 stimuli. A strip of the paper was therefore exposed for an hour or two to 

 the spectrum, but without any sensible effect, the whole surface being equally 

 reddened by an acid. As this experiment sufficiently indicated the action of 

 light, if any, to be very slow, I next placed a strip, partly covered, in a south- 

 east window, where it remained from June 10 to August 1!», receiving the few 

 and scanty sunbeams which that interval of the deplorable summer of 1841 

 afforded. When removed, the part exposed could barely be distinguished from 

 the part shaded as a trifle yellower. But on applying acid the exposed and 

 shaded portions were at once distinguished by the assumption of a vivid red 

 in the latter and the former remaining unchanged. 



A mezzotinto picture was now pressed on a glazed frame over another por- 

 tion of the same paper and abandoned on the upper shelf of a greenhouse to 

 whatever sun might occur from August 19 to October 19. The interval i)roved 

 one of almost uninterrupted storm, rain, and darkness. On removal no appear- 

 ance whatever of any impressed picture could be discerned, nor was it even 

 possible to tell the top of the picture from the l)ottom. It was then exposed in 

 ^ glass jar to the fumes of muriatic acid, when, after a few minnutes, the 

 development of the dormant picture commenced and slowly proceeded, disclosing 

 the details in a soft and pleasing style. Being then laid by in a drawer, with 

 free access of air, the picture again faded by very slow degrees, and on January 

 2, 1842, was found quite obliterated. Being then subjected to the acid vapor, 

 the color was reproduced. 



Viola odorata. — Chemists are familiar with the color of this flower as a test 

 of acids and alkalies, for which, however, it seems by no means better adapted 

 than many others ; less so, indeed, than that of the Viola tricolor, the common 

 purple iris, and many others which might be named. It offers, in fact, another 

 and rather a striking instance of the simultaneous existence of two coloring 

 ingredients in the same flower, comporting themsleves differently, not only in 

 regard to light but to chemical agents. Extracted with alcohol, the juice of the 



