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complete, but the parts of the work relating to sensitometry and to development oxidation have now been completed, and have yielded some interesting information relating both to the behaviour of the developer and to the chemistry of its mode of action. The work is to be published in detail in the appropriate journals and in a paper of this nature there is time to refer only to some of the data obtained.
II. THE MECHANISM OF THE ELON-HYDROQUINONE DEVELOPER
Before going on to discuss the data obtained, an outline will be given here on the conclusions reached in this work regarding the mechanism of the Klon-hydroquinone developer3. This is done not because it will be of immediate practical use to the laboratory controllers, but rather in the hope that it will provide a thread on which the data and relationships to be described below may be strung together.
The most important conclusion to be drawn from this work, was that the Elon-hydroquinone developer shows a phenomenon of super-additivity when
aON ..th HYOROQUNO*.
C »JEBTU» POIHT
Fig. I. The course of development of motion picture Fig. 2. The length of the toe of
positive film (exposed to the 17th step of the Eastman the characteristic curve is mea
IIB sensitometer) when treated at pH 10.0 in the fol sured by the Log E displacement
lowing developers : 0.032 M Hydroquinone (lowest (AB) of the curve from the straight
curve), 0.008 M Elon (middle curve), and 0.008 A1 Elon line at the Inertia point,
plus 0.032 M hydroquinone. At any level of density, the slope of the Elon-hydroquinone curve is greater than the sum of the slopes of the other two.
one considers rates of development. In Fig. 1 the density of a given exposure step on a piece of film is plotted against time of development. One curve shows how the density grows in a hydroquinone developer, and the other curve shows how the density grows in an Elon developer. The third curve, standing well above the other two, shows how the density grows in a developer which contains the same amounts of Elon and hydroquinone that were present in the separate developers (other things being maintained equal) . It will be seen that at a given stage of development, that is at a given density, the rate of development in the Elon-hydroquinone developer is greater than the sum of the rates of development in the separate Elon and hydroquinone developers.
This super-additivity phenomenon, which is the basis of the superiority of the Elon-hydroquinone developer, results from a two-stage development process. The Elon is, in fact, the active developing agent. This reacts with the silver bromide and becomes oxidised. In the normal way, in the absence of hydroquinone, the oxidised Elon would be converted to Elon sulphonate by reaction with the sulphite in the developer. However, when hydroquinone is present, the hydroquinone regenerates Elon by reducing