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This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1911 edition. Excerpt: ...is calculated as gelatin. The thimble is next Soxhlct extracted with petroleum ether or benzene, the distillate evaporated to dryness and weighed. If a continuous film is being examined the residue is usually a vegetable oil, as castor, added to impart flexibility to the film. The odor of camphor in the benzene-extract points to the presence of celluloid or similar pyroxylin plastic. If the film from a photographic plate is under examination, the presence of rubber used to edge the plate must be looked for in the benzene-extract. The benzene-insoluble residue in the fat thimble is probably pyroxylin, with or without cellulose acetate. Filtration of hot amyl acetate through the thimble dissolves cellulose nitrate and does not affect cellulose acetate, whereby a separation of these two may be made. The presence of gelatin in the " support " in the film may be determined qualitatively by placing a drop of nitric acid on the film, which coagulates and turns the gelatin yellow, while at the same time dissolving the cellulose nitrate.1 1. According to E. Valenta (Atelier phot., 16, 3) photographic papers shouM consist chiefly of best rag stock, though most are principally purified cellulose: they must contain practically no metallic particles, since these are the chief cause of spots. The author's method of testing faulty silver bromide paper is: (1) dot the back with 5% aniline sulphate, when imperfectly purified cellulose will turn the dots yellow; (2) expose under negatives, and an additional piece in strips, one to five seconds, to a IG-c.p. lamp at 1m.; these will show the general properties of the emulsion and the degree of spotting; (3) exposure of a piece to daylight will sometimes show violet spots, which arc caused by dust and turn...
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