07 Dec




















not to wear anything that may produce the effect spoken of-- dark dresses always being the best. The action of light both combines and decomposes bodies. For instance, chlorine and hydrogen will remain in a glass vessel without alteration if kept in the dark; but if exposed to the rays of the sun, they immediately enter into combination, and produce hydrochloric acid. On the other hand, if colorless nitric acid be exposed to the sun, it becomes yellow, then changes to red, and oxygen is liberated by the partial decomposition effected by the solar rays. Of the organic substances none are more readily acted upon by light than the various combinations of silver. Of these some are more, and others less sensitive. If Chloride of silver, which is a white precipitate formed by adding chloride of sodium (common salt) to a solution of nitrate of silver, be exposed to diffused light, it speedily assumes a violet tint, and ultimately becomes nearly black. With iodide of silver, bromide of silver, ammonio-nitrate of silver, and other salts of this metal, the result will be much the same. Some bodies, which under the influence of light, undergo chemical changes, have the power of restoring themselves to their original condition in the dark. This is more remarkably displayed in the iodide of platinum, which readily recieves a photogenic image by darkening over the exposed surfaces, but speedily loses it by bleaching in the dark. The ioduret of Daguerre's plate, and some other iodides, exhibit the same peculiarity--This leads us to the striking fact, that bodies which have undergone a change of estate under the influence of day-light have some latent power by which they can renovate themselves. Possibly the hours of night are as necessary to inanimate nature as they

Comments
* The email will not be published on the website.
I BUILT MY SITE FOR FREE USING