Photographic Chemistry; With Numerous Engravings and Diagrams

Photographic Chemistry; With Numerous Engravings and Diagrams

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1906 edition. Excerpt: ...easily ionised cyanide, thus liberating HCN, which forms easily soluble AgH(CN), . Intensification, .--Intensification is, of course, the opposite to reduction. Extra material is added to a weak negative, in order to increase its density. In most cases the silver image is first bleached by immersion in mercuric chloride solution. This bleaching is due to the formation The Ferricyanide Reducer.--In Howard Farmer's process a freshly-made solution of potassium ferricyanide and sodium thiosulphate is used for reduction. By this method the silver is slowly converted into ferrocyanide, and it is very probable that small quantities of the ferricyanide are formed at the same time. Both compounds, however, dissolve at once in the sodium thiosulphate, thus allowing the amount of reduction to be observed. The following reactions take place: --of a mixture of silver and mercurous chloride, thus: --Ag2 + 2HgC'-l2 = 2AgCl + Hg, Cl2 Men-uric Mercurous chloride. Y clIloi'l(l(!. As this whitened image is hardly opaque enough for printing, it' is darkened either by treating with ammonia, ammonium sulphide, sodium sulphide, or with a ferrous oxalate developer. The Blazrlsening Action of Am-monia.--A dilute solution of ammonia blackens the image, probably by the formation of complicated mercurous and silver derivatives of ammonium chloride; the two chief compounds being NH, Hg, Cl and NHAgHg._.Cl. From some recent investigations of M. F. Leteur the black compound, on analysis, contains silver, and these experiments confirm the formula NHAgHg, Cl proposed by Chapman Jones. The equation showing the change would then be--1' In the case of using ammonium sulphide the metals forming the bleached image are converted into sulphides. 2AgCl + 2Hg, Cl2 more

Product details

  • Paperback | 42 pages
  • 189 x 246 x 2mm | 95g
  • United States
  • English
  • black & white illustrations
  • 1236793188
  • 9781236793188