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240 CINEMATOGRAPHIC ANNUAL
velopability except when there was contact between the grains. Davidson 10 found grains in certain emulsions tending to develop in pairs or large clumps. This effect was particularly noticeable in high speed emulsions.
The effects just cited may or may not be sufficient to account for all of the grain clumping observed as graininess of photographic deposits. In any case much practical benefit can be derived from observations leading to a way of minimizing or avoiding graininess even if the causes are not all immediately apparent.
Callier27 had used the relation between diffuse and specular densities as an indication of grain size but this had not been found to serve as a measure of graininess. With these facts in mind Jones and Deisch1 started out to measure graininess resulting from exposure and development of different products with varied conditions. They chose as their measurement of graininess the distance at which a magnified image of the deposit has to be viewed to appear uniform instead of appearing structured, i.e., grainy. Suitable checks and methods of standardization were introduced to make the measure finally obtained the same for different observers. These same methods were used again by Hardy and Jones28 for further study of motion picture negative and positive emulsions. Crabtree29 preferred to judge graininess by comparing prints on positive film processed to equal densities and projected in quick time succession, using experienced observers to judge relative graininess in the test. Landau30 devised a comparator for comparison of the specimen with a series of photographic enlargements of grainy deposits. Conklin31 arranged a comparison microscope in such manner as to permit the relative magnification of the two fields to be changed at will and thus allow the relative graininess of an arbitrary standard and a sample to be compared by observing the relative magnification for equal appearance of graininess. Since all of these recent methods are based only upon some form of comparison of samples among themselves or with an arbitrary standard, a qualitative agreement is the most that can be expected.
Jones and Deisch1 found the graininess of the deposits depending, in general, upon the density of the deposit, the developer used, the gamma to which development was carried and upon the original emulsion tested. The largest effect with a chosen emulsion was the increase of graininass with density, though in some cases, notably with paraphenylene diamine, the graininess reaches a maximum and then decreases. This particular developer has been noted for its fine grain and reduced graininess, but is hardly to be considered commercial because of excessive exposures and development required with it. Amongst developers of such characteristics as to be considered commercially, considerable differences were noted in the graininess of the deposits produced, a pyro formula appearing, perhaps, slightly the best of those tested. Fast emulsions were found to have greater graininess than slow, as would be expected from the experimental fact that they have as a class the larger original silver-bromide grains. The concentration of bromide in the developer, the temperature of