280 Mr. Hunt on Actino-Chemistry^ 



is owing to the separation of oxide of silver*;" and this opi- 

 nion has been very generally entertained. I am satisfied, 

 however, that something more than this takes place, and that 

 an actual combination of the organic body with the silver en- 

 sues; and I hope to have an opportunity of examining some 

 of the very complicated phaenomena which have presented 

 themselves to my notice, during investigations which have 

 been made incidentally to the present inquiry, into the influ- 

 ence of organic matter upon the salts of silver and gold, during 

 exposure to light and heat. 



16. Count Rumford appears to have been the first who no- 

 ticed that carbon had the property of reducing the salts of 

 gold and silver from their solutions, at a temperature below 

 that of boiling water in the dark ; and that the same precipi- 

 tate of pure metal took place by exposure to the sun's rays. 

 He inferred from this, that the "chemical properties attributed 

 to light" were due alone to the heating powers of the sun's 

 rays. The error of this has long been known, as experiments 

 with the prismatic spectrum have shown that the rays in which 

 the calorific power exists at its maximum have little effect in 

 producing any such reduction. The precipitation of the silver 

 from the nitrate in solution takes place very speedily under 

 the influence of the solar rays which have been deprived of 

 their heat by being passed through plates of alum or rock- 

 salt, and when the temperature of the solution is kept at 

 32° F. '; 



17. Nitrate of silver dissolved in distilled water was spread 

 on paper ; it was allowed to darken to a chocolate-brown : 

 ammonia now dissolved off* the darkened surface, proving it 

 to be in the condition of an oxide. The exposure being con- 

 tinued for some hours during very bright sunshine, a surface 

 of a peculiar russet colour, and of a dirty appearance, resulted. 

 Ammonia did not now possess the power of altering the co- 

 lour; it removed some oxide from the paper, which arose 

 from undecomposed nitrate of silver, protected by the super- 

 ficial film from the action of the rays of the sun. But if the 

 darkened paper was previously soaked in distilled water, 

 until ail the free nitrate was dissolved out of it, neither am- 

 monia nor dilute nitric acid separated any oxide, clearly 

 showing that the darkened surface was metallic silver. 



18. Some nitrate of silver in distilled water was boiled with 

 a grain or two of animal gelatine for some hours in the dark ; 

 the solution became coloured a fine brown, but even after 

 standing for many hours no precipitation took place. Potash 

 precipitated the oxide of a black colour, which ammonia dis- 



* Turner's Elements of Chemistry. 



