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Silver Bromide

action, potassium and yellow

SILVER BROMIDE (Formula, AgBr.; molecular weight, i88; synonym, bromide of silver).— Prepared by direct union of the two elements silver and bromine, or by double decomposition between silver nitrate and any soluble bromide. In the Daguerreotype process, silver bromide is formed by the first method, and in the dry-plate process by the second, potassium or ammonium bromide being used. When silver nitrate is added to potassium bromide, the silver combines with the bromide, and the nitrate with the potassium.

Silver bromide usually occurs in a yellowish state. Stas in his researches proves it to occur in six distinctly different states. These are—(c) as white flakes, (2) as yellow flakes, (3) as a bright yellow powder, (4) as a pearly white powder, (5) as a yellowish white powder, (6) in an intense yellow melted state.

Dr. Pitteurs classifies the photographically useful varieties of silver bromide as follows*: Silver bromide is insoluble in water, alcohol, ether, and in weak ammonia solution. Soluble

in sodium hyposulphite, potassium cyanide, ammonia, and in saturated solutions of the majority of the chlorides, bromides, and iodides.

Bromide of silver is sensitive to light, darkening by a lengthy action to a dirty gray, bro mine being evolved.

By very short exposures to light no visible change takes place, although a most important action in reality occurs. This action is usually stated to be a reduction to silver sub-bromide, Ag,Br. Others consider it to be converted into an oxybromide 2AgBr, or into a photo salt{ AgBrz.yAg,Br. Whatever the precise action may be, it is a fact that it is more easily reduced by certain salts, alkaline pyro and other substances blackening it, which fact constitutes the pro cess of development.

Its uses in photography, in the collodion and dry-plate emulsion processes, are very im portant.