File:The American annual of photography (1922) (14778434211).jpg

Identifier: americanannualof36newy (find matches)
Title: The American annual of photography
Year: 1922 (1920s)
Authors:
Subjects: Photography
Publisher: New York : Tennant and Ward
Contributing Library: Harold B. Lee Library
Digitizing Sponsor: Brigham Young University

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evelopment werecarried on while the plate was still wet. Various experiments lead Schoenbein to the conclusionthat the developing agent which best reduced the haloid actedupon by light to metallic silver was a ferrous sulphate solution(Fe SO4). After development the plate was immersed in astrong solution of potassium cyanide, which dissolved all thefree silver not acted upon by the light. Owing to its highlypoisonous quality potassium cyanide was soon replaced bysodium thiosulphate commonly known as hypo which pro-duced the same chemical action as potassium cyanide. The chemical reaction which takes place in the process ofdevelopment may be expressed as follows: Fe SO4 + Ag Br = Ag + Fe SO^ Brthis reaction depositing pure metallic silver Ag upon thesurface of the plate. In the process of fixation using hypo as the chemicalmedium the following reaction takes place:— 2 Ag Br + 3 Na^ S O3 = 2 Na, Br + Ag Na (S.OJi■—Soluble.A practical test of the chemical reaction as well as the 76
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FRACTURE OF FIBULA SHOWING DISPLACEMENT AND OVER-RIDING OF FRAGMENTS.Radiograph Taken Through Cast. Illustrating article Photography as Applied to Radiography, by S. A. Schwars. n reduction to metallic silver may readily be performed asfollows: Take 25 cc of nitrate of silver in solution.* To this add anequal amount of water. In a separate container dissolve afew grains of Metol, Pyro or any of the commonly employeddeveloping agents. Upon mixing the two liquids a heavyblack precipitate is formed which is pure metallic silver. A simple chemical experiment which readily illustrates thereducing power of Hypo may be performed as follows: To a solution of 50 cc of nitrate of silver add 25 cc of asaturated solution of sodium chloride (common kitchen salt).Immediately a heavy white precipitate—silver chloride—isformed. If Hypo is added 5 cc at a time while stirring thesilver chloride it will be seen that the latter gradually disap-pears—goes into solution. In modern days when the keepi

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