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416 Transactions of S.M.P.E., Vol XIII, No. 38, 1929
used alone, it does not have sufficient reducing power to start the development. If development is started in an Elon developer, however, it can be completed wdth one containing only hydroquinone as the reducing agent.
2. Sodium Sulfite. This salt is an organic reducing agent and protects the developing agents from oxidation by the oxygen absorbed from the atmosphere. Its solubility in the developer formula is such that the concentration of sulfite can be increased from zero to more than 200 grams per liter. An increase in concentration above 100 grams per liter slightly decreases the rate of development partly because of its solvent action upon the silver halide in the emulsion. This solvent action is of the utmost importance from the standpoint of graininess and will be discussed later.
3. Borax. This chemical is used because it is a very mild alkali and gives a developer with very low alkalinity when used with a mixture of Elon, hydroquinone, and sodium sulfite.
F. Effect of Varying the Concentration of the Developer Constituents
The rate of development, speed of emulsion, fog, graininess, etc., produced by the borax developer can be altered by changing the relative concentrations of the constituents used in the developer and by the addition of other chemicals such as potassium bromide, hypo, and sodium sulfate. Several experimental developers were compounded in an attempt to decrease the rate of development without decreasing the speed of the emulsion or increasing the fogging action. The tests were made with a small developing apparatus, but with the same technic as used in commercial work. H. & D. curves were made for the various development times and the gamma values determined as shown in Table II. The fog values and Eastman speed are given for a gamma value of 0.70. The same roll of Eastman panchromatic negative film was used for all of the tests. The type of H. & D. curve obtained with this emulsion is shown in Fig. 1. The developers are arranged roughly in the order in which they were tested and in terms of the extra constituents which were added.
1. Effect of Varying the Concentration of the Developing Agents. It is possible to double the concentration of Elon and hydroquinone in the regular borax formula. This increase produces