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Engravings can be thus copied almost instantaneously, and camera views obtained in one or two minutes on almost any preparation of silver. The common sulphate of copper solution has the same property. III. CHROMATYPE. Many efforts have been made to render chromatic acid an active agent in the production of photographs. M. Ponton used a paper saturated with bichromate of potash, and this was one of the earliest photogenic processes. M. Becquerel improved upon this process by sizing the paper with starch previous to the application of the bichromate of potash solution, which enabled him to convert the negative picture into a positive one, by the use of a solution of iodine, which combined with that portion of the starch on which the light had not acted. But by neither of these processes could clear and distinct pictures be formed. Mr. Hunt has, however, discovered a process which is so exceedingly simple, and the resulting pictures of so pleasing a character, that, although it is not sufficiently sensitive for use in the camera, it will be found of the greatest value for copying botanical specimens, engravings, or the like. The paper to be prepared is washed over with a solution of sulphate of copper--about one drachm to an ounce of water--and partially dried; it is then washed with a moderately strong solution of bichromate of potash, and dried at a little distance from the fire. Paper thus prepared may be kept any length of time, in a portfolio, and are always ready for use. When exposed to the sunshine for a time, varying with the intensity of the light, from five to fifteen or twenty minutes, the result is generally a negative picture.