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28 BRUNNER, MEANS, AND ZAPPERT July
just before the end-point it disappears and is replaced by the same orange-pink indicator color observed in the metol-hydroquinone titration. Another few drops of reagent produce the usual indicator color change.
Determination of Sodium Sulfite and Bisulfite
The bisulfite used in developer A-605 is converted to sulfite by the sodium carbonate. The same analytical procedure for the sulfite ion is, therefore, applicable to both developers. Atkinson and Shaner5 and Stott4 have described a procedure in which an acidified standard icdine solution is titrated with the developer. This method may be used for these developers except that a weaker iodine solution should be used for developer A-605 since it contains a very small amount of sulfite ions. The only precaution required is that sufficient acid be present to keep the solution below pH 4 during the entire titration and thus prevent oxidation of the developing agents.
This method was found to be accurate to 100.4 =t 2.0 per cent for concentrations ranging from 50 per cent less to 25 per cent more than the concentrations normally used.
Determination of Sodium Carbonate
Evans and Hanson6 described a procedure in which carbon dioxide and sulfur dioxide are liberated by acidification of the developer, the sulfur dioxide is then oxidized to sulfate and the remaining carbon dioxide is measured volumetrically. Atkinson and Shaner5 determined carbon dioxide by absorption in soda lime or Ascarite. A simpler method described by Stott4 involved the potentiometric titration of the developer with standard acid using glass or platinum and calomel electrodes. In this titration, the first inflection point in the titration curve corresponds to the change of carbonate to bicarbonate, but because of the buffering action of the sulfite present, this inflection is not at all sharp.
We have found it easier and faster to titrate the developer directly with standard acid to about pH 4 (gray color of methyl orange-indigo carmine) at which point the carbonate has been completely neutralized and the sulfite has been converted to bisulfite. By deducting the volume of acid required for the sulfite present, the carbonate content may be calculated. Since developer A-605 has no alkalinity due to sulfite, no deduction is required. This method of determining carbonate was found to be accurate to 99 =±= 1 per cent.