THE HISTORY OF SOME DISCOVERIES OF PHOTOGRAPHY. 307 



stvength. It tlien becomes very sensitive and easily receives a j)hoto- 

 graphic image. If the pkite be cold, the sensibility is considerably 

 lower. The image obtained is fixed by washing with hyposnlphate 

 of soda and finally with water. 



SECTION V. INSTANTANEOUS PROCESS. 



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 Atheiuemn Decem- 

 ber 0, 1851. An experiment was tried in flune. at the Royal Institu- 

 tion, in which an instantaneous image was produced; l)ut as the 

 process Avas the subject of another patent it was not published nntil 

 the above date. The experiment in question was that of obtaining 

 a j)hotograi)hic copy of a printed paper fastened to a wheel, wdiich 

 was made to revolve as rapidly as possible, by illuminating it for 

 a moment by the light obtained from the discharge of a Leydeii 

 battery. The bill was faithfully jirinted, not even a letter being 

 indistinct. 



A glass plate is emj^loyed, and Mr. Talbot thus directs that it 

 should be ])repared : 



1. Take the most licpiid portion of the white of an eg'^, rejecting 

 the rest. Mix it with an equal quantity of Avater. 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 invisil)le. 



2. To an aqueous solution of nitrate of silver add a considerable 

 quantity of alcohol, so that an ounce of the mixture may contain 3 

 grains of the nitrate. I have tried various proportions, from 1 to C) 

 grains, but perhaps ."i grains answer the best. More experiments are 

 here required, since the results are much influenced by this part of the 

 i:)rocess. 



3. Dip the plate into this solution, and then let it dry spontaneously. 

 Faint prismatic colors will then be seen upon the plate. It is impor- 

 tant to renuirk that the nitrate of silver appears to form a true chem- 

 ical combination with the albumen, rendering it much harder and 

 insoluble in licjuids which dissolved it previously. 



4. Wash with distilled water to remove any superfluous portion of 

 the nitrate of silver. Then give the jjlate a second coating of albu- 

 men, similar to the first, but in drying avoid heating it too much, 

 which Avould cause a commencement of decomposition of the silvei-. 



5. To an aqueous solution of proto-iodide of iron add, first, an 

 (•(jual volume of acetic acid, and tlien 10 volumes of alcohol. Allow 

 the mixture to repose two or three days. At the end of that time 



