the Photographic Image, ; 191 
will be better investigated after a full knowledge of the first has 
been acquired. 
The fact of chlorine being evolved during the decomposition 
by solar agency of chloride of silver under water, has been repeat- 
edly observed and is fully corroborated by my own experiments. 
It follows, therefore, that if a solution of nitrate of silver be em- 
ployed in conjunction with the chloride, as in the ordinary prac- 
tice of photography, the evolved chlorine will exert its own 
peculiar action on the silver solution in contact, precipitating 
from it an additional amount of white chloride, which im turn 
becomes, partially at least, decomposed by light. It has been 
assumed that the whole of the nascent chlorine is thus available 
for the formation of new chloride of silver ; but this can, I think, 
be true only if other matters are present having the power to 
decompose hypochlorous acid, a product always formed to the 
amount of half that of the available chlorine, according to the 
reaction first pomted out by Balard, 
C+ AgO, NO’=AgCl+C10+NO*. 
It might then be predicted that, by exposing pure white chlo- 
ride of silver under a solution of the nitrate of known strength, 
this latter would become continually weakened. This I find to 
be the case; and in the event of employing a dilute solution, 
every trace of silver is removed, leaving only mixed nitric and 
hypochlorous acids as residual products dissolved in the water. 
It is possible also to remove the metal from a solution of nitrate 
of lead, by exposure to sunlight in contact with recently pre- 
cipitated chloride of silver. 
Again, inasmuch as the white chloride darkens with a rapidity 
regulated by the energy with which the liberated chlorine is re- 
moved from its sphere of influence, I have been able to prove* 
that reducing agents, the protochloride of tin especially, as also 
certain alkaline solutions, greatly facilitate the decomposition ; 
while the higher chlorides of platinum and mercury are known 
to exert a power in the opposite direction. 
Several experiments were also made upon the chloride of silver 
formed by the direct union of its elements—silver-leaf, electro- 
plated daguerreotype tablets, and the silver specula obtained on 
collodionized glass by the ordinary photographic processes ; 
these several conditions of silver, converted into chloride by the 
action of chlorine gas, furnished products all of which suffered 
decomposition on exposure to sunshine, but were very much less 
speedily affected than the condition of precipitated chloride 
* “On the alteration of Chloride of Silver by Light,” Photographie 
News, October 1859. 
