352 HANDBOOK OF PHOTOGRAPHY 



sideration of developers having more than one reducing agent, which will, in general, 

 have unequal temperature coefficients. Here it appears probable that one reducing 

 agent will be affected more than the other with consequent variation in the final result. 

 For small variations from standard temperature, time compensation for temperature 

 change may be used even in this case, though it may be impossible for large variations. 

 In view of all these factors, it is the best policy to hold developing temperatures 

 to standard values where good reproducibility and uniform high quality are required. 

 Many mechanisms and devices have been suggested to secure this desirable result 

 under the extremely wide range of conditions and equipment encountered. 



Table I. — Developing Time at Various Temperatures 



Time at temperature / 



The most common device in use is a water bath. In small or improvised dark- 

 rooms this may take the simple form of a large tray or tank filled with water of the 

 desired temperature in which the developing tray or dish is set in such manner as to 

 be as completely surrounded as possible. In more elaborate installations the same 

 principle is used, but frequently the water in the bath is itself circulated, agitated, 

 and thermostatically controlled to uniformly maintain the correct temperature. 



In other systems, coils are used to secure the heat transfer from developer to 

 thermostatically controlled systems as required to maintain uniform temperatures. 

 This is most common in the largest installations, such as the motion-picture processing 

 laboratories where jacketed tanks having the required capacity of several hundred 

 gallons would be unnecessarily expensive. 



The most common requirement of these systems is ability to cool the solution, for 

 the desired developing temperature is often 65 or 68°F., either of which is below usual 

 room temperatures in the common installations. Surprising as it may seem, members 

 of the second Byrd Antarctic Expedition report that this cooling of developer was one 

 of their difficult photographic problems while staying at Little America. Their water 

 supply was melted snow, and, after melting and passing through the pipes in the rooms 

 warmed for their habitation, cool water was at a premium. Where a supply of cool 

 water is available, the simplest procedure is to cool the bath with a stream of it, as 

 needed to maintain the desired temperature. The ability to use this means is seasonal 

 in many places, and hence more elaborate means are often required, particularly under 

 summer conditions. 



With present-day perfection of small units of mechanical refrigeration, they have 

 been quite generally introduced for the control of medium- to large-sized installations. 

 The general scheme of control has to be fitted to the specific equipment, and accord- 

 ingly the details will differ. Temperature changes during processing and washing are 

 undesirable; hence it is usually desirable when making an installation of this type to 

 provide for the control of all the processing baths and the wash water as well as of the 

 developer itself. 



