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as if the salt of silver, being slightly aflfeeted by the light, 

 though not in a degree to produce any visible effect on it if 

 alone, sets up a catalytic action, which is extended to the 

 salts of iron, and which continues after the stimulus of the 

 light is withdrawn. The catalysis which then takes place 

 has induced me to name this process, for want of a better 

 word, the Catalysotype. Sir J. Herschelland Mr. Fox Talbot 

 have remarked the same fact with regard to other salts of 

 iron, but I do not know of any process being employed for 

 photographic purposes which depends on this action for its 

 development, except my own. 



My reason for using the muriatic acid solution, previous 

 to washing with the ioduret of iron, is this : 1 was for a long- 

 time tormented by seeing the pictures spoiled by yellow 

 patches, and could not remedy it, until I observed that they 

 presented an appearance as if that portion of the nitrate of sil- 

 ver which was not decomposed by the ioduret of iron had 

 flowed away from the part. I then recollected that Sir J. 

 Herschell and Mr. Hunt had proved that iodide of silver is 

 not very sensitive to light, unless some free nitrate be pre- 

 sent. I accordingly tried to keep both together on the paper, 

 and after many plans had failed, 1 succeeded by steeping it in 

 the acid solution, which makes it freely and evenly imbibe 

 whatever fluid is presented to it. I am sure that its utility is 

 not confined to this effect, but it was for that purpose that I 

 first employed it. My reason for adding the tincture of iodine 

 to the syrup is, that having in my first experiments made use 

 of, with success, a syrup that had been for some time pre- 

 pared, and afterwards remarking that fresh syrup did not an- 

 swer so well, 1 examined both, and found in the former a 

 little free iodine ; I therefore added a little tincture of iodine 



a camel-hair pencil, or by immersion. The picture must then be well washed 

 in water, to remove the fixing material, which would cause it to fade by expo- 

 sure to light. 



H 2 



