the Photographic Image. 189 
A substance having the composition specified in the second 
column, cannot be referred to any probable formula, but would 
appear to be composed of a mixture of silver with unaltered 
chloride, in about the proportion that would result from the 
destruction of two only in every seven parts of white chloride 
submitted to the action of the sun’s rays. This, as already 
stated, represents the extent of decomposition on the average 
product ; but special experiments, in which the nitrate of silver 
was employed in greater excess, and the chloride solution un- 
usually dilute, enabled me to prepare, on the very brilliant day, 
June 16th, 1857, a product containing more than 82 per cent. 
of silver, and in which it might be assumed that one-third of the 
total amount of white chloride operated upon had become re- 
duced to the metallic state. In attempting to pass this stage, 
the mechanical difficulty of the reduced silver particles encrusting 
and offering protection to the undecomposed white chloride, 
presents an obstacle which only extreme dilution and excessively 
fine state of division seem likely to combat. 
In the application of the several chemical reagents by which 
it was proposed to eliminate the portion of unaltered chloride in 
admixture, and thus to isolate the essential matter which con- 
stituted the darker residual portion, it was found impossible to 
arrive at any other conclusion than that of its consisting of pure 
silver: throughout the examination no evidence was presented 
which pointed to the existence of the so-called subchloride of 
silver, or at least of its production under these circumstances ; 
but, on the contrary, it appeared to be uniformly proved that the 
metal, somewhat modified in colour and physical condition by 
the varying circumstances of the experiment, was in every case 
the product resulting from the action of light upon the chloride 
of silver. 
The reactions more particularly examined were the following:— 
Ammonia dissolved out from the substance the whole of the 
unaltered chloride (afterwards recovered in a white scaly form 
by the evaporation of the solvent), while it left insoluble a 
grey residue of metallic silver in which no chlorine could be 
found. 
Cyanide of potassium solution dissolved away the chloride and 
left metallic silver. 
Hyposulphite of soda, employed in the form both of concen- 
trated and dilute solutions, speedily dissolved out in the cold 
the unchanged chloride, leaving a residue of grey metallic silver, 
which contained neither oxygen, chlorine, nor sulphur. 
Iodide of potassium operated first in the conversion of the 
chloride into yellow iodide of silver, which, on adding an excess 
of the reagent, was entirely taken into solution. The grey 
