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the oxidised Elon before this latter can be sulphonated. The oxidised hydroquinone forms hydroquinone sulphonate by reacting with the sulphite. In other words, the function of the Elon may be described as that of an intermediary between the hydroquinone and the silver bromide, carrying electrons from one to the other. As the alkalinity of the developer is increased, the reduction potential of the hydroquinone increases more rapidly than that of the Elon and, therefore, as the alkalinity increases, the most active combination of Elon and hydroquinone will contain less and less Elon.
III. EXPERIMENTAL CONDITIONS
In the motion picture field the Elon-hydroquinone developer is used for processing both negatives and positives. Different formulae are used for
pH= 870
_- -"-"IS
vo
pH = 9.80
1
,;>--:
20 40 60 eo too o
20 40 60 SO IOO O MOLE PERCENT ELON
20 40 60 eo
Fig. 3. The Log E value of the Inertia point for negative film at a gamma of 0.65 is plotted as a function of the molar percentage of Elon in the total quantity of developing agent (0.057 M) in the
negative type developer. No bromide, solid curves ; Ig. per litre KBr, . 2g. per litre
KBr, — . — . — . Series in which the sulphite concentration was varied from the normal 100 g. per litre are indicated by the appropriate concentration numbers, e.g., — I
these two purposes, but the essential difference between them is to be found in the pYL value. Negative developers have a pH value of about 9.0 and positive developers have a pYL value of 10.0 — 10.5. There are secondary differences in the sulphite and bromide concentrations. In order to carry out a survey of the properties of the Elon-hydroquinone developer, it was necessary to find a typical formula to work on.
Developer Formulae
In the case of negative developers the choice was easy, because almost all laboratories use a developer of the type of D76, the formula of which is :
Grams Moles
Elon
2.0 .0116 1 total developing 5 0 .0454 J agent = .057 M
Hydroquinone
Sodium sulphite (anhyd.)
100
Borax...
2.0
Water
1 litre