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solution by the film by a sort of adsorption process. The developing agent which is adsorbed and removed is lost from the point of view of doing any useful development wrork. This means that a tank of developer will become exhausted even when completely unexposed film is run through it.
At higher pH values, see Fig. 7, the proportion of Elon consumed greatly diminishes, and in developers containing less than 30% of the developing agent as Elon, the amount of Elon consumed in the development is almost negligible and the hydroquinone bears almost all the whole brunt of the oxidation.
The relative rates of consumption of Elon and hydroquinone are not affected by a change in the sulphite and bromide concentrations.
VI. DISCUSSION AND NOTES ON ANALYTICAL PROCEDURES
Tet us now recapitulate some of the salient points from the preceding matter. We will discuss also some points on the methods of analysis.
VARtttTiOM of pH
p8«8 7
pH . 30
VfHRlfVTSOri OF BR0H»E COMCfcHTRftTlOM AT p\\ z «J-0
+ 10 CM. «h/UTU
1 2-0 ««• Kftv A.ITM.
I VfAitfliOrt OF SuuPHt« coric"
25 OKI Ma.SOj /LITRE »T pH.0 o
ORPItiRTE > [GM.H3LS]»I0'* Of DEVELOPIHG t\(t£HT USJfc UP Pfc* (<SM. ATOM] « I0"* 0?
SILVER F0U«». ©HtBROQUmOMl.eJLOfl , — TOTAL
ft&SCISSW > ELOK COMCtKT«*Tior< m % OF TOTBL »«L0W«6 «.£nT l«lTinLL"< PRCSUiT.
Fig. 6. Relationship between developing agent consumption and initial concentration.
The Elon-hydroquinone developer is typically composed of :
Elon
Hydroquinone Sulphite Alkali (as pK) Bromide
Iodide is deliberately omitted from this list in spite of the fact that in recent years, there have been claims4 that the equilibrium concentration of iodide is sufficiently large to be significant in used motion picture negative and positive baths. The author's own findings5, however, indicate that the concentration of iodide in normal baths is negligible.
Elon and Hydroquinone
In general terms, and especially at pH levels above 9.6, an increase in the proportion of Elon leads to increased inertia speed without having any influence on the shape of the toe of the curve. In the absence of bromide at pK 9.0, there is an optimum ratio of Elon, corresponding roughly to that