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26 BRUNNER, MEANS, AND ZAPPERT July
TABLE I First Developer— A-502
Water, 65 to 90 degrees Fahrenheit 750 milliliters
Metol 3 grams
Sodium Sulfite 50 grams
Hydroquinone 6 grains
Sodium Carbonate Monohydrate 40 grams
Sodium Thiocyanate 2 grams
Potassium Bromide 2 grams
Water to make 1 liter
Color Developer— A-605
Water, 65 to 70 degrees Fahrenheit 750 milliliters
Calgon 1 gram
Sodium Bisulfite 2 grams
Diethyl-p-Phenylenediamine Hydrochloride 4 grams
Sodium Carbonate Monohydrate 67 . 5 grams
Potassium Bromide 1 gram
Water to make 1 liter
Determination of Metol and Hydroquinone
The first developer used in the Ansco color process is similar to the usual reversal first developer containing sodium thiocyanate.
All the earlier methods for the determination of metol and hydroquinone were based on two separate extractions of the developing agents and possessed several disadvantages, one of which was the determination of metol by difference. Baumbach2 made a definite advance in 1946 by describing a single methyl acetate extraction method involving a potentiometric acid titration of metol followed by oxidation of both metol and hydroquinone with iodine. Shaner and Sparks3 modified this by using a U-tube extractor and methyl ethyl ketone as solvent. The difficulty in determining the end point in the iodine titration is a disadvantage common to both methods. When the pH is maintained at 6.5 to 7.0, the solution is so highly colored by oxidation products that it is extremely difficult to see the blue starch-iodine end-point. Oxidation at low pH values results in a nearly colorless solution, but the iodine oxidation is not quantitative.
Because of the small sample used in the Shaner and Sparks procedure, the volume of acid needed to titrate the metol is very small. Four developers, cited by these authors, containing 2.0, 3.0, 0.22, and 0.31 grams of metol per liter, require only 1.16, 1.74, 0.13, and 0.18 milliliters of 0.1 normal acid when determined in accordance with their