I v.— C HEMISTEY 



Art. LXI. — On certain Results obtained upon some of the Argentiferous Salts 

 wJdch are affected by Lujht. By William Skey, Analyst to the Geolo- 

 gical Survey Depaitment. 



[Read before the Wellington Philosophical Society, Wth October, 1879.] 

 It 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 photographic 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 thuik, 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. 



3. 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. photographic 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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