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reaches a maximum or an optimum value at a fairly low proportion of Elon. It is interesting to note that this assessment confirms the selection of the D76 formula for giving high speed. The addition of bromide, shown by the dotted curves, greatly reduces the speed obtainable at all three pH levels and at all Klon/hydroquinone ratios. Reducing the sulphite concentration at pH 9.0 also reduces the inertia speed.
Rate of Development for Negative Film
The time of development required to reach the gamma value of 0.65 is shown in Fig. 4 and decreases with increasing proportion of Elon.
Inertia Speed for Positive Films
The critical gamma was taken at the rather low value of 2.0 in order to include as many data as possible in the assessment. This does not affect the
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Fig. 5. The Log £ value of the Inertia point and the time of development, for positive film at a gamma of 2.00, are shown as a function of the molar percentage of Elon in the total quantity of developing
agent (0.04 M) in the positive type developer. No bromide, solid curves ; \g. per litre KBr, ;
2g. per litre KBr, —.—.—. Note : at pH 10.0, with 2.0g. per litre of KBr, the critical gamma could be reached at a certain time of development and again, with greater emulsion speed, after a longer development when the increasing fog had caused the gamma to decrease after an optimum value had been reached.
general picture. The inertia speed shown in Fig. 5 increases markedly with increasing proportions of Elon. In the absence of bromide the critical gamma can only be reached at low Elon/hydroquinone ratios.
Rate of Development for Positive Film
The time of development required to reach a gamma of 2.0 is shown in Fig. 5. It reaches a minimum value at a proportion of Elon that decreases with increasing pK, in keeping with the mechanism outlined earlier.
Toe Displacement
Examination of the figures for the toe displacement shows that at a given gamma the toe displacement is independent of the Elon/hydroquinone ratio, and of the other variables. This contradicts the widely held view, that the shape of the toe can be influenced by changing the Elon/hydroquinone ratio.