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Fine-Grain Developers — Cavlion and Crahtree 431
With contiiiiioiis machine development the sludge may aecumnlate in the bottom of the tank or tnbes as a result of insufficient agitation of the developer. By circulating the developer through a storage tank, most of the sludge settles out in this tank. The suspended silver can also be removed by filtering through a bed of sawdust. The sawdust for this purpose must be extracted with boiling water before use to remove the soluble constituents which might change the characteristics of the developer. The various factors which determine the amount of sludge formation are discussed later under " graininess. "
IV. Graixiness of Images De^-eloped ix the Borax Developer
Several investigators have studied the fine grain producing properties of the Eastman borax developer. Its ability to produce finegrained images is undoubtedly a result of the presence of a high content of sodium sulfite which exerts, a solvent action on the silver lialide grains reducing their size and preventing clumping. ^^ Namias^^ concludes that the rate of development is too low for practical purposes and claims that his recommended developer (formula 13, Table VI) gives equally fine-gained images with an increase in rate of development. Lumiere and Seyewtz^^ found that the images produced by borax developer are finer-grained than those produced by the same developing constituents used with carbonate as the alkali. Veldman^* concluded that the borax developer gave very fine-grained images but no finer than the following developer : Eton 15 grams ; sodium sulfite (anhydrous) 150 grams; potassium bromide 2 grams; water to 1 liter. This developer is impractical because of the loss in emulsion speed caused by the high bromide content. He varied the sulfite content from 0.5 to 320 grams per liter and found that the graininess decreased as the sulfite content increased. Luppo-Cramer^^ found that with the Eastman borax developer fine-grained images were not obtained with all silver bromide emulsions. Emmermann^in a series of tests on motion picture film found that the Eastman borax developer w^as the best formula known for ])roducing finegrained images. Nauck-^ concludes that the low alkalinity of the borax developer contributes indirectly to the production of finegrained images because the relatively low rate of development permits the sulfite to exert more solvent action which progresses witli time. Although the normal borax developer formula gives satisfactory fine-grained images, experiments w^ere made to determine the