A Manual of Photography Author:George Dawson Purchase of this book includes free trial access to www.million-books.com where you can read more than a million books for free. Excerpt from book: Section 3best way of avoiding such decompositions will be described in the practical portion of this work treating of Positive Printing. Cyanide Of Potassium As A Fixing Agent.—This salt is most... more » energetic in dissolving' the textit{haloid salts of silver, far more so than Hyposulphite of Soda. It is generally used textit{h? fixing negatives and positives developed on collodionized glass, but, on account of its very powerful action on sub-salts or organic salts of silver, is totally unsuited for fixing Positives on paper. Even when a developer has been used, unless the solution of Cyanide is tolerably dilute, it is apt to attack the image, converting it superficially into Cyanide of Silver, and then dissolving it in the form of a double Cyanide of Potassium and Silver. The solvent powers of this Cyanide on metallic silver are greatly increased by the addition of a little Iodine to its aqueous solution. A colourless liquid is thus obtained which has been termed " Iodo-»yanide of Potassium." Sulphoctanides As Fixing Agents.—Sulphocyanides of Potassium and Ammonium have been proposed, and to some extent used, as fixing agents for positives on paper. They resemble the alkaline chlorides used for this purpose, inasmuch as their solvent power textit{depends on the degree of concentration of the solution, but they greatly exceed the latter salts in their power of dissolving the insoluble Salts of Silver, when strong solutions are used. Though inferior to Hyposulphites in this varying degree of solvent power, they have the advantage of imparting no Sulphur to the print, and they preserve the tones clear and free from mealiness. Photographic Objectives Or Lenses. It would swell the pages of this Manual beyond the allotted bounds to discuss the nature and properties of Light and the principles involved in the con...« less