THE illSTOKY OF SOME DISCOVERIES OF PHOTOGRAPHY. 307 



streiiirth. It then becomes very sensitive and easily receives a photo- 

 graphic inia<i^e. If the })hite be cohl, the sensibility is considerably 

 lower. The iinai>e obtained is fixed by washing with hyposulphate 

 of soda and fin;dl\- with water. 



SECTION V. INSTANTANEOUS PROCESS. 



The next iincntion and j)ateiit of Mr. Fox Talbot possesses many 

 jxH-nliarities, and as the resnlts are of a remarkable character it is 

 important that the process slionld be given nncui-tailed in its main 

 particulars. The following description mnst be regarded as an 

 abstract of Mr. Talbot's communication to the Athena'um Decem- 

 ber ('), 1S51. An experiment was tried in June, at the Royal Institu- 

 tion, 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 olitained from the discharge of a Le3^deii 

 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 Avitli 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 3 

 grains of the nitrate. I have tried various proportions, from 1 to 6 

 grains, l)ut perhaps 3 grains answer the best. More experiments are 

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

 process. 



3. Dip the j^late into this solution, and then let it dry spontaneously. 

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

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

 ical 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 jjlate a second coating of albu- 

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

 wdiich 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 10 volumes of alcohol. Allow 

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



