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1950 SIMPLIFICATION OF PROCESSING METHODS 19
film types, the limitations and peculiarities of equipment, and to meet the chemical and economic requirements of replenishment and silver recovery. Additional information on the chemistry of rapidly acting baths will be found in a series of papers by J. I. Grabtree and his associates11"14 on rapid processing and on low and high-temperature processing.
Because of the short times and intense agitation used in practice, preliminary tests with hand manipulation are of limited assistance in selection of chemical bath formulas, and should be followed by tests on a typical element of the machine design under consideration before final decisions are made. For example: the characteristic curve may show a drooping shoulder with quiet immersion development; high fog may be caused by excessively slow transfer from developer to rinse, insufficiently rapid renewal of rinse water, or lack of agitation in rinsing; yellow stain which may be difficult to eliminate in hand tests without use of an acid stop bath is easily overcome in the machine by forceful spray rinsing with water.
An unusual characteristic of the current variable-density soundrecording film was observed when high-activity hydroquinone or Elon-hydroquinone developers were adopted for rapid processing. When development in these baths was carried to the point where the normal low-contrast curve was obtained with low-intensity exposures, a contrasty continuously upcurving characteristic was found with high-intensity short time exposures such as are used in sound-recording or in kinescope photography. The effect was observed at 70 F as well as at higher temperature. Normal curve shape was obtained by the addition of 10 g of sodium thiosulfate per liter to the rapid developer. The effect of exposure intensity level on curve shape with normal developers is very small.
It has been supposed that excessive consumption of developer might occur with spray application of warm developer. In practice, this is not a serious problem since the air in a small developer cabinet is insufficient to oxidize any large amount of sulfite, and renewal of air can be kept small by the use of the tight seals which are required for other reasons. Nevertheless, troublesome aerial fog was encountered in one case, even when extra precautions were taken to reduce the amount of air leakage. This difficulty was eliminated when the developer alkalinity was lowered a few tenths of a pH unit below the critical point for aerial fog propensity — near 12.0 — found by H. D. Russell and M. D. Little, of these Laboratories (private communication).
In connection with the increasing use of spray application of de