The preparation and properties of some synthetic photohalide emulsions

(1) A method of preparing photohalide emulsions somewhat different from that of Lüppo-Cramer has been worked out, using either colloidal silver or colloidal silver sulphide as the sensitizer.(2) Treatment of the plates containing this emulsion with chromic acid to remove excess colloidal silver also lowers sensitivity considerably. This sensitivity can be restored by an after-treatment of the plates with a very dilute ammonia solution.(3) The photohalide emulsion prepared as described showed, with one exception, a broader spectral sensitivity than those prepared without colloidal silver or silver sulphide. This agrees with the previous work of others on photohalide emulsions.(4) The spectral sensitivity of such emulsions differs from those sensitized with allyl-thiourea sensitizer in being more sensitive in the red and less sensitive in the green region of the spectrum.(5) The present work supports the strain-ionic deformation hypothesis of sensitivity proposed by Sheppard, Trivelli and Loveland. It does not, however, exclude the hypothesis of Hickman as to the role played by the silver sulphide sensitizing speck.     

The action of hydrogen peroxide on photographic gelatino-silver halide emulsions

1. The sensitometric characteristics of photographic plates exposed to hydrogen peroxide and developed are strikingly similar, both for time of exposures, time of development, and intensity i.e., concentration). Characteristic curves similar to H. and D. curves were obtained, including a period of “reversal.”2. A tentative theory of the action of hydrogen peroxide is suggested. It is supposed that the decomposition of peroxide is chemi-luminiscent, short wave-length radiation being afforded at the surface of the silver halide grain, and particularly at check the hypothesis that these nuclei consist of colloid silver.The authors desire to express their thanks to Mr. R. F. Quirk and Mr. E. Huberth for painstaking assistance in the experi- mental work, and to Miss Anber J. Benedict for making the pH measurements.