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o 
as if the salt of silver, being slightly affected 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light is withdrawn.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. Herschell and 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. S 
My reason for using the muriatic acid solution, previous 
to washing with the ioduret of iron, is this: I 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. 1am 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 
_ acamel-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 
