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 solution of hydrochloric acid. The print is then rinsed and dried. To prevent injury to the gelatine film, which would become further soluble by the action of light, it is rendered wholly insoluble by any of the known methods, such as immersion in a solution of alum, bichloride of mercury, &c. This process has not hitherto been successfully worked.

In the same communication, M. Poitevin, mentioned another mode of carbon printing. Paper treated with perchloride of iron and tartaric acid, without pigment or gelatine, is exposed under a positive cliché. The parts treated with these salts possess the power of precipitating casein, which, after insolation, they lose. The coloring matter is therefore mixed with milk, and the exposed print immersed in it; the casein, and pigment with it, are precipitated on the protected parts, which form the blacks of the picture.

Early in 1863, Mr. Pouncy called attention to a new mode of carbon printing, which he had patented in the previous January. In the course of the summer the details were published, and were found to embrace an important new principle in carbon printing, inasmuch as the picture was formed of a fatty ink, similar to that used in ordinary mechanical printing. Thin, transparent paper, like tracing paper, was coated with a mixture of carbon or other pigment, fatty matter, such as tallow or oil, bichromate of potash, or bitumen of Judæa, or both, and turpentine, or some equivalent body. When