Abstract
IN the September number of the Astrophysical Journal Mr. R. J. Wallace gives an account of his investigation of the circumstances that control the size of the silver particles in a developed gelatino-bromide plate. Of four rapid plates of American make, the “Seed 27, Gilt Edge” was found to give the best results. It was the most uniform in speed from time to time, and gave the least amount of “chemical fog,” the smallest particles of silver, and the most regular distribution of them. While the particles were found to be, generally speaking, spherical in ordinary plates, isochromatic plates of several makes showed the peculiarity of having almost exclusively elongated (the author calls them “spicular”) grains at the surface of the film, while in passing downwards through the film they gradually gave place to rounded particles, until close to the supporting glass these latter were the only ones found. Intensification increases the size of the particles; this is the common experience of those interested in these matters, but the author's demonstration is of special interest, as he performed the intensification with a brush, using the mercury and ammonia method, without shifting the plate, so that he was able to photograph the identical particles before and after the operation. The same grains can easily be traced in the two photographs reproduced. The magnification is 430 diameters. The author also shows the difference between rapid and slow development. In the first case he considers that the silver particles most nearly approach the size of the original particles of silver salt from which they are produced, while by prolonged development they become enlarged by reason of the formation of “group-particles” as well as by accretion. For the finest grain the author deprecates slow development. In a postscript reference is made to the deduction of Messrs. Lumiere and Seyewetz from their recent experiments to the effect that neither the temperature, concentration, nor duration of development practically affects the size of the grain. The author considers that these investigators have neglected the formation of “group-particles” because they dissolved off the film after development and examined a new film made from the product.
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The Grain in Photographic Films . Nature 70, 571 (1904). https://doi.org/10.1038/070571a0
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DOI: https://doi.org/10.1038/070571a0