The American annual of photography (1922) (14781584695)

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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cipitate.He further proved that upon adding ammonia in some formor other, the black precipitate was changed into an insolubleresidue which upon examination was found to be puremetallic silver. Subsequent experiments by Thomas Wedgewood, SirHumphry Davy, Dr. Wollaston, Niepce and Daguerre demon-strated the possibility of coating a highly polished surfacewith Nitrate of Silver and upon this surface producing animage by means of the rays of light. The silver plate which Daguerre used as a support for thesensitive coating of his then famous Daguerroeotype wassoon replaced by a glass plate coated with albumen whichacted as a vehicle for the silver salts. Later the albumenwas replaced by a collodion emulsion which in turn was soonsupplanted by a coating of gelatine. This last process isstill in use at the present day. Generally speaking the emulsion or sub-stratum is evenlyspread over the plate and when it has sufficiently hardenedthe sensitive salts are introduced. The chemicals used in 74
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FOOT OF CHILD. SPACES SHOWING AREAS NOT YET OSSIFIED. Illustrating article Photography as Applied to Radiography, by S. A. Schwars. 7^ order to render the emulsion sensitive to the actinic raysof Hght are the following: Ag NOs^Silver Nitrate. KBr =Potassium Bromide. KI = Potassium Iodide. In the making of the plate the following reaction takes place Ag NO3 + KBr = KNO3 + Ag Br (i) and Ag NO3 + KI = KNO3 + Agl (2) Upon exposure to light the plate undergoes certain chemicalchanges which are invisible and remain so until the plate isdeveloped, that is to say the latent image is brought to thesurface. The first plate (glass) which had an emulsion on it, wasthe wet plate, and was first used practically by Schoenbein,a Swiss chemist. The vehicle employed for the purpose ofcarrying the sensitive coating was ordinary cotton dissolvedin nitric and sulphuric acids better known as collodion. Thisplate after.having been coated with collodion was immersedin a silver bath and both exposure and deve