IV—CHEMISTRY. 
Art. LXI.—On certain Results obtained upon some of the Argentiferous Salts 
which are affected by Light. By Wurm Sxey, Analyst to the Geolo- 
gical Survey Department. 
[Read before the Wellington Philosophical Society, 11th October, 1879.] 
Ir may be known, although I can get no direct intimation of this, that 
iodide of silver, like the chloride, requires the presence of water or its 
constituents ere photographie effects can be induced upon it; but, whether 
or no, a description of the results which I have obtained in connection with 
this point will be, I think, of some interest to you, and I therefore give one, 
and attach thereto a statement of other results obtained with these sub- 
stances bearing upon the mode in which this photographic effect is pro- 
duced :— 
1. Iodide of silver is not photographically affected even by direct sun- 
light, if it is kept the while at a temperature approaching to 100? C. ; the 
presence of water or aqueous vapour here does not affect the result. 
2. At a temperature of 100? C., and in presence of water, chloride of 
silver, on the other hand, darkens—though but slowly—in direct sunlight. 
In aqueous vapour, at about 160? C., it does not darken. 
8. A strong aqueous solution of sodic-chloride in contact with these 
silver salts renders them impervious to the action of light, even at common 
temperatures. 
4. At a temperature approaching 100? C. photographie effects produced 
upon argentic-iodide are obliterated. 
5. A considerable quantity of pure argentic-iodide, after being stirred 
in the light till it became of a light colour, did not either lose or gain in 
weight thereby,—that is, appreciably to me. At 100? C. its colour became 
a full yellow, relapsing to a pale tint when cooled to a common temperature. 
6. The product of sunlight upon even pure argentic-chloride varies 
-both in colour and composition according as to whether this compound is 
alkalized or not. Thus, in a weak solution of potash, the product is of a 
very dark brown or black colour, and this is permanent under the circum- 
stances. In weak acetic or hydrochloric acid, it evolves gas (probably 
oxygen), and acquires a pale red colour. A large volume of distilled water 
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