Light blackens silver chloride

Diammino-silver nitrate forms glistening rhombic or prismatic crystals which blacken on exposure to light. It is fairly stable, and may be heated to 100° C. without loss of ammonia. Further heating causes it to decompose, and finally to melt with evolution of nitrogen and ammonia, leaving a residue of metallic silver and ammonium nitrate. It is soluble in water, but partial dissociation takes place so that the solution is alkaline in reaction, and it therefore yields a precipitate of silver chloride and soluble chlorides. Certain of the metals—for example, zinc, cadmium, and copper—quickly reduce the ammine in solution to metallic silver. 

Bergman found that silver and mercurous oxalates blacken in sunlight. Scheele found that metallic silver is formed in silver chloride blackened by light, and that it grows black sooner in the violet than in any of the other rays , the first distinction of the different chemical effects of light of different colours. He seems to have known of Schulze s work. ... 

After several partial reports (by Priestley, Bergmann, Scheele, Ingenhousz), Senebier publishes a comprehensive and successful book on the effect of solar light on plants, oils, dyes, wood, etc. This not only mentions that silver chloride blackens at light but also that this darkening depends on the color of the light. 

With chloride ions, Ag+ yields a white precipitate of silver chloride that blackens in bright light. It is easily solubilized... 

White, odorless, tasteless, heavy powder slowly dec by sunlight into mercuric chloride and metallic mercury sublimes at 400-500 without melting, d 7.15. Practically insol in water (0-00020g/]00 ml H20 at 25 ) HCI or alkali and alkaline earth chlorides increase soly in water. Insol in alcohol. ether. Dec by solns of alkali iodides, bromides or cya -nides into the mercuric salt and metallic mecury solns of alkali chlorides act similarly but slowly. It is blackened by ammonia, caustic alkali and alkaline earth solns. Protect from light. Incompat Bromides, iodides, alkali chlorides, sulfates, sulfites, carbonates, hydroxides, lime water, acacia, ammonia, golden antimony sulfide, cocaine, cyanides, copper salts, hydrogen peroxide, iodine, iodoform, lead salts, silver salts, soap, sulfides. 

They give, with caustic fixed alkalies, a brown precipitate with ammonia, a similar one, soluble in the slightest excess with hydrochloric acid, or any soluble chloride, the white curdy precipitate of chloride of silver, insoluble in water and acids, but soluble in ammonia and with sulphuretted hydrogen, a dark brown, nearly black precipitate of sulphuret. Silver and all its compounds are very sensitive to sulphuretted hydrogen, which blackens them. Most of the compounds of oxide of silver are very soluble in ammonia and all the compounds of silver are darkened by the actjon of light, a property which has lately been applied to useful purposes in the Daguerreot3ipe, Calotype, and other photographic methods. Oxide of silver is reduced to the metallic state from its solutions by copper, zinc, and several other metals. When mercury is used, there is formed a heautiful arborescent crystallisation of an alloy of silver and mercury, called Arbor Dianae. 

Nitrate of silver, or lunar caustic, is very much used as an escharotic. It is made by dissolving pure silver, or the oxide formed from the chloride (see p. 213) in nitric acid and evaporating, when crystals are deposited, which are fine tables, anhydrous, and fusible at 426 , when they may be run into a mould so as to yield the sticks of caustic. Formula Ag 0, NOj, or Ag, NOj. It is the chief ingredient of indelible ink. Like all the other compounds of silver, it is blackened by light, especially when in contact with organic matter. It is much used as a test for chlorine. 

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