808 THE HISTORY OF SOME DISCOVERIES OF PHOTOGRAPHY. 



it will have changed color, and the odor of acetic acid, as Avell as 

 that of alcohol, will have disappeared, and the liquid will have 

 acquired a peculiar but agreeable vinous odor. 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 moder- 

 ate daylight, avoiding, however, the direct solar rays. 



7. A solution is made of nitrate of silver, containing about 70 grains 

 to 1 ounce of Avater. To 3 parts of this add 2 of acetic acid. Then, 

 if the prepared plate is rapidly dipped once or twice into this solu- 

 tion, it acquires a very great degree of sensibility, and it ought then 

 to be placed in the camera without much delay. 



8. The i^late is Avithclrawn from the camera, and in order to bring 

 out the image it is dipped into a solution of protosulphate of iron 

 containing 1 part of the saturated solution diluted with 2 or 3 parts 

 of water. The image appears very rapidly. 



9. Having washed the plate Avith Avater, it is noAv placed in a solu- 

 tion of hyposulphite of soda, Avhich in one minute causes the image 

 to brighten up exceedingly by removing a kind of veil which pre- 

 A^iously coA'ered it. 



10. The plate is then Avashed Avith distilled Avater and the j^rocess 

 is terminated. In order, hoAvever, to guard against future accidents 

 it is well to giA^e the picture another coating of albumen and A^arnish. 



These operations may aiipoar long in the tlesoription, but tbey 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 prop- 

 erty of iodide of iron, which was discovered by Doctor ^^'oods, of Parsontown, 

 in Ireland; and that of sulphate of iron, for which science is indebted to the 

 researches of Mr. Robert Hunt. In tlie true adjustment of the proportions and 

 in the mode of operation lies the ditficulty of these investigations, since it is 

 possible by adopting other proportions and manipulations not very greatly dif- 

 fering 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 desir- 

 able 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 hail, hoAvever, been adopted pre- 

 viously, at Mr. Talbot's recommendation, by Sir John Herschel, and 

 in the collodion processes, to be by and by described, Ave liaA^e similar 

 phenomena, to which the name applies wnth equal force. 



It is not improbable that the high degree of sensibility Avhich is 

 certainly obtained in this process is rather due to the formation of an 

 iodide of ethyl in the mixture than to the combination, as Mr. Talbot 

 supposes, of the proto-iodide and the proto-sulphate of iron. My 

 ow^n researches convince me that Ave should seek for the highest 

 degrees of sensibility amidst the numerous combinations of the 

 ethyl and methyl compounds Avith the metallic oxides. 



