[EXPERIMENTS ON THE COLORED FILMS]
FORMED BY IODINE, BROMINE, AND CHLORINE
UPON VARIOUS METALS.
BY AUGUSTUS WALLER, M. D.
In a paper presented by me to the Academy of Sciences of Paris, an extract from which may be seen in the Comptes Rendus for October 5, 1840, I first demonstrated the error committed in ascribing to the iodide of silver alone the power of fixing the vapors of mercury, after it had been exposed to the action of light. Instead of this property being exclusively confined to a film of iodide of silver, as obtained in the process of M. Daguerre, I found that it existed in many other substances when presented to the action of light in the state of thin films, viz. by the bromide and chloride of silver; by the oxide, bromide, iodide and chloride of copper, and some others; all these, however, possessing less sensibility than the iodide of silver of Daguerre, and therefore less available for the reproduction of the images of the camera than the compound originally discovered by that gentleman. The iodide of Daguerre was found already too little sensitive to the influence of light in this climate, especially when applied to the reproduction of the image of animate objects, so that those films discovered by me seemed still less suitable to be employed for that purpose; this objection has, however, been completely removed by recent improvements, more particularly those of M. Claudet, who effected this principally by combining the original discovery of Daguerre with those mentioned above as having been subsequently made by myself. Pursuing the first stage of Daguerre's process, he obtained the film of iodide of silver, and added to this another film of bromide, either in a simple state,—as practised in my experiments published more than six months before—or after two of these substances had been combined together, as the chloride of iodine and the bromide of iodine, which he was the first to employ.
These colored films, however, merit attention independently of the purposes to which they may be applied in photography: the beauty of some of the phenomena themselves is peculiarly attractive; the numerous changes of color they undergo, either by a variation in the thickness of the film, or by the action of light, assign them a place among the most curious facts of science, and the extreme facility with which they are obtained adds to the interest they excite.
Impressed with these ideas, I was induced to pursue a train of investigation on this subject; among the results of which, one of the most interesting was a new method of making colored rings, like those generally known under the name of "Newton's colored rings," on many of the metals, by the same chemical process as that employed for forming the films of uniform thickness in photography. In order to procure these colored rings, and at the same time to show the identity of the origin of the colors with those of the ordinary transparent films, that is, as residing simply in the thickness of the lamina and not dependent on the ordinary cause of color, we have but to place a piece of iodine on a well-polished surface of silver or copper, and in a short time we find around the iodine a series of colored zones of the various tints of the spectrum, and approaching in a greater or less degree to the form of a circle, according as they have been more or less disturbed in their formation by currents of the surrounding air. In order that they may be perfectly regular, as large as possible, and with tints undisturbed by the action of light, it is necessary to place a piece of iodine in the centre of a well-polished plate, as before described; this is then to be shaded by an opake screen superimposed a few lines from the surface to cause the vapors which would otherwise ascend and partially escape, to expand over its silver surface. Colored rings may be formed in the same manner by bromine and chlorine and the various combinations of these bodies with each other, except that for those that are gaseous or liquid it is requisite to pay a little attention to the manner of disengaging them on the surface of the metal, either by passing them through a glass tube, or by some other contrivance easy to execute.