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August 24, 1883.] THE PHOTOGRAPHIC NEWS 535 The third, consisting of chloride only, was prepared in the tollowing proportions:— Silver nitrate Sodium chloride Opaque gelatine Hydrochloric acid Water ... 200 grains ... 160 „ ... 30 „ ... 1 minim ... 5 ounces Adding after emulsification— Opaque gelatine 100 grains Nelson’s No. 1. 140 „ Water 5 ounces These three emulsions were put into separate flasks of the same shape and size ; they were simultaneously immersed in the same cooking vessel, and boiled for exactly the same Comparative T'iew of the Ffect of Variation in the Proportion of Iodide in Fmultiono. Number of Plate and nature of Emulsion. Ordinary Pyro Developer. Sulphite Developer. Oxalate Developer. Plate 1— Portion coated with AgBr ... Slightly denser than rest of plate. Ditto, ditto, AgBr+2-5°/AgI Greater contrast. 1 Ditto, ditto, AgBr-|-5 0 / 0 AgI Greater contrast; shadows clearer NB. All three parts of the image ! flashed out simultaneously. Traces of green fog. No green fog; shadows clearer than above. No green fog; shadows still clearer. All three parts developed simul taneously. Denser than rest of plate. ) Apparently under-developed; ( shadows clearer than above ; f image browner by reflected > light. The pure bromide was the first to develop. Plate 2— Portion coated with AgBr ... Ditto, ditto,AgBi'4-8%AgI... Ditto, ditto, AgBr-+10°/AgI Band of green fog visible by re flected light denser than rest of plate, and better exposed. 1 No green fog ; distance and 1 shadows clear, bnt slightly J undet-exposed. Parts with iodide troublesome to fix. Green fog over whole plate, but more pronounced in thia por tion. ) Rather slower in development; F green fog decreases as iodide J increases. Each division of the plate clearly marked by bands of green fog. Denser than rest of plate. ' Shadows clearer, but colour of r film by reflected light J slightly greener. Each division clearly marked by reflected light. Plate 3— Portion coated with AgEr ... Ditto, ditto, AgBr-+14°/AgI Ditto, ditto, AgBr +18°/AgI Denser than rest of plate; no fog of any kind. Best portion of plate, distance very clear. Rather under-exposed. Each division of plate plainly marked by quality of negative. Denser than rest; slightly better detail; slight green fog. Slower in development; no green fog. •Slightly less density. Not so much difference in quality of each division. Quicker in development, and denser than rest of plate. ) Shadows clearer; colour of - image browner by reflected 1 light. Better result than with the other developers. Plate 4— Portion coated with AgBr ... Ditto, ditto, AgBr-+210/AgI Ditto, ditto, AgBr-250/AgI Too dense; slight green fog; over-developed. ) Shadows and distance much > clearer; no fog; not so dense ) as above. As iodide increases, difficulty of fixing becomes troublesome. Too dense; muchgreenfog; deve lops quicker than rest of plate. ) Not so much density, less green F fog, and far clearer shadows J and distance than above. Iodide parts take 5 or 6 times as long to fix as the pure bromide. Very dense ; develops quicker than rest of plate. ) Very marked difference; shad- C ows much clearer; colour of ( image browner by reflected ) light Ear superior negative to those developed by pyro. Dense, good detail; perfect negative. j Thin, no detail, but no fog F anywhere ; apparently much J under-developed. Plate 5— Portion coated with AgBr .. Ditto, ditto, AgBr-290/AgI Ditto, ditto, AgBr+330/AgI Green fog, but good density; slightly quicker in development j No green fog ; clear shadows; ( plenty of detail, and far ( better negative on the whole ) than above portion. Much quicker in development; twice as dense as iodide parts. ) Clear shadows and very great C contrast, but deficient in ( density; colour of image ) browner by reflected light. All parts seemed equally deve loped on looking at the back before fixing. Plate G— Portion coated with AgBr ... Ditto, ditto, AgBr4-66"/ 0 AgI Ditto, ditto, AgBr-1000/Ag No green fog; good detail; per fect negative. { Clearer shadows and distance, but not so much detail, and image too thin. 2nd and 3rd portions indistin guishable from one another. Slight green fog; good density. ) Clearer shadows, and not quite C such density as above, but fa> ( less difference than might bi ) expected. No green fog. Each division clearly marked by decrease in density. Much quicker in development; Very dense. ) Much clearer shadows, but - rather thin; image much ) browner by reflected light. Each division clearly marked by decrease in density. length of time. All the other operations were conducted in a manner precisely the same for each bath, so that the emulsions, although prepared separately, should have the same properties as when made together in one and the same flask. Of course there is one possible source of error in this method, inasmuch as there may be some mutual reaction of the mixed haloids upon one another daring emulsification, which could not possibly be the case when boiled in sepa rate flasks. Having then prepared the emulsions, plates were coated in the manner previously described. One-third of each plate was always coated with pure bromide ; the next divi sions were covered with gradually increasing proportions of chloride or iodide. The proportions were calculated by