The next 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 Athenúum, Dec. 6, 1851. An experiment was tried in June, at the Royal Institution, in which an instantaneous image was produced; but as the process was the subject of another patent, it was not published 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, rejecting 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 considerable quantity of alcohol, so that an ounce of the mixture may contain three grains of the nitrate. I have tried various proportions, 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 spontaneously. 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, rendering it much harder, and insoluble in liquids which dissolved it previously.
4. Wash with distilled water to remove any superfluous portion of the nitrate of silver. Then give the plate a second coating of albumen similar to the first, but, in drying, avoid heating it too much, which would cause a commencement of decomposition of the silver.
5. To an aqueous solution of proto-iodide of iron add, first, an equal volume of acetic acid, and then ten volumes of alcohol. Allow the mixture to repose two or three days. At the end of that time it will have changed colour, and the odour of acetic acid as well as that of alcohol will have disappeared, and the liquid will have acquired a peculiar but agreeable vinous odour. It is in this state that I prefer to employ it.
6. Into the iodide thus prepared and modified, the plate is dipped for a few seconds. All these operations may be performed by moderate daylight, avoiding, however, the direct solar rays.
7. A solution is made of nitrate of silver, containing about 70 grains to one ounce of water. To three parts of this add two of acetic acid. Then, if the prepared plate is rapidly dipped once or twice into this solution, it acquires a very great degree of sensibility, and it ought then to be placed in the camera without much delay.
8. The plate is withdrawn from the camera, and in order to bring out the image, it is dipped into a solution of protosulphate of iron, containing one part of the saturated solution diluted with two or three parts of water. The image appears very rapidly.
9. Having washed the plate with water, it is now placed in a solution of hyposulphite of soda, which in one minute causes the image to brighten up exceedingly, by removing a kind of veil which previously covered it.
10. The plate is then washed with distilled water, and the process is terminated. In order, however, to guard against future accidents, it is well to give the picture another coating of albumen and of varnish.
" These operations may appear long in the description, but they are rapidly enough executed after a little practice. In the process which I have now described, I trust that I have effected a harmonious combination of several previously ascertained and valuable facts, especially of the photographic property of iodide of iron, which was discovered by Dr. Woods, of Parsonstown, in Ireland ; and that of sulphate of iron, for which science is indebted to the researches of Mr. Robert Hunt. In the true adjustment of the proportions, and in the mode of operation, lies the difficulty of these investigations, since it is possible, by adopting other proportions and manipulations not very greatly differing from the above, and which a careless reader might consider to be the same, not only to fail in obtaining the highly exalted sensibility which is desirable in this process, but actually to obtain scarcely any photographic result at all".
Mr. Talbot proposed the name of Amphitype, or doubtful image, for these pictures. This name had, however, been adopted previously, at Mr. Talbot's recommendation, by Sir John Her-schel, and in the Collodion processes, to be by-and-by described, we have similar phenomena, to which the name applies with equal force.
It is not improbable but the high degree of sensibility which is certainly obtained in this process, is rather due to the formation of an iodide of ethyle in the mixture, than to the combination, as Mr. Talbot supposes, of the proto-iodide and the proto-sulphate of iron. My own researches convince me that we should seek for the highest degrees of sensibility amidst the numerous combinations of the ethyle and methyle compounds with the metallic oxides.
The last invention of Mr. Fox Talbot is one by which he obtains etchings of objects ; the images of which are produced by radiant action upon steel plates. This process, and analogous ones by others, will be described in Part III.