Silver chloride light-sensitive compounds

All the silver halides are sensitive to light, decomposing eventually to silver. In sunlight, silver chloride turns first violet and finally black. The use of these compounds in photography depends on this (see below). (All silver salts are, in fact, photosensitive—the neck of a silver nitrate bottle is black owing to a deposit of silver.)... 

The white film that appeared on the cards when you took them out of the silver nitrate solution was the substance that made the cards sensitive to light. The white film, which was so thin you may not have actually seen it, was silver chloride, a compound that resulted from the reaction between the sodium chloride and the silver nitrate. The equation for the reaction is ... 

Compounds that contain silver—such as silver chloride, silver iodide, and silver bromide—are highly sensitive to light. When... 

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. 

Hyposulphite of soda, and other soluble salts of hyposulphurous acid, possess the remarkable property of dissolving all the compounds of silver, even the chloride, and the solution thus formed has a very intense sweet taste, with a metallic after-taste. This property has been made available in the dagaerreotype, for the purpose of dissolving the sensitive coating of iodide from the plate of eilver alter exposure to light, aud thus fixing the image already formed. For this purpose hyposulphite of soda is now prepared on a very considerable scale. 

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