A Manual Of Photography

32 HISTORY OF PHOTOGRAPHY. respect to this part of the invention, the patentee claims the production of a photographic image upon a plate of steel. Upon a careful examination of this patent, it will he evident that the substitution of porcelain for glass, with very doubtful advantage, constitutes its only real novelty, excepting the process of using potash above described by Mr. Malone. The images on oiled paper are said to be exceedingly good, and this may prove to be a valuable suggestion, of which however we had a modification already in the waxed paper. Section V.—Instantaneous Process. The last invention and patent of Mr. Fox Talbot possesses many peculiarities, and as the results are of a remarkable character, it is important that the process should be given uncurtailed in its main particulars. The following description must be regarded as an abstract of Mr. Talbot's communication to the Athenæum, Dec. 6, 1851. An experiment was tried in June, at the Boyal Institution, in which an instantaneous image was produced; but as the process was the subject of another patent it was not pub- lished until the above date. The experiment in question was that of obtaining a photographic copy of a printed paper fastened to a wheel, which was made to revolve as rapidly as possible, by illuminating it for a moment by the light obtained from the discharge of a Leyden battery: the bill was faithfully printed, not even a letter being indistinct. A glass plate is employed, and Mr. Talbot thus directs that it should be prepared. 1. Take the most liquid portion of the white of an egg, re- jecting the rest. Mix it with an equal quantity of water. Spread it very evenly upon a plate of glass, and dry it at the fire. A strong heat may be used without injuring the plate. The film of dried albumen ought to be uniform and nearly invisible. 2. To an aqueous solution of nitrate of silver add a conside- rable quantity of alcohol, so that an ounce of the mixture may contain three grains of the nitrate. I have tried various pro- portions, from one to six grains, but perhaps three grains answer best. More experiments are here required, since the results are much influenced by this part of the process. 3. Dip the plate into this solution, and then let it dry spon- taneously. Faint prismatic colours will then be seen upon the plate. It is important to remark, that the nitrate of silver appears to form a true chemical combination with the albumen,