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688 LEVENSON Decernber
of developing agents, would only save money if the hydroquinonesulfite price ratio is 40 : 1 or more. At a ratio of 30 : 1 the most economical sulfite concentration would be reached at 80 grams per liter. At a -ratio of 20 : 1 the most economical sulfite concentration in the bath •would. be. QQ grams per liter. At a ratio of 10: 1 the most economical concentration of sulfite would be 45 grams per liter.
Although the numerical values in the above example were chosen to illustrates the case of the L-R Spray machine, the shape of the curves and tfee general conclusion are probably valid for any case involving the aerial oxidation of an Elon-hydroquinone developer at pH 10 and at 20 degrees centigrade when the hydroquinone-Elon ratio is sufficiently high for the hy droquinone to be predominantly lost. . . . ;
V. CONCLUSION
Practical experience by the motion picture processing laboratories shows that a spray or jet-applied developer can be maintained over a Considerable period by suitable replenishment. The present work indicates that the cost of the chemicals wasted by aerial oxidation depends upon the volume of developer used in the installation. If the minimum volume of developer is used, e.g., about one twentieth of the volume that would be required in a normal total-immersion system of the same production capacity, then it is cheaper to use a spray system with a negative developer at pH. 9. This arises from the fact, now presented* that the autoxidation rate in a developer of this type reaches a maximum value at a comparatively low degree of aeration. When the volume of the developer in a spray system is about one sixth of the volume in an equivalent total-immersion machine, having a fair degree of aeration, the two systems will cost about the same to replenish. At equal volumes, aerial oxidation in the spray system will waste 3 to 4 times as much developing agent and sulfite as in any normal system.
At the other end of the range, at pH. 10.5, a spray-developing machine will cost about twice as much in developing agent and sulfite wastage as any normal machine, and, at equal volumes, it can cost over six times as much.
An interesting point emerging from this work is the very small, or negligible, rate of aerial oxidation in a system where, in spite of a vigorous stirring of the solution, no bubbles of air were carried below the surface. — •The figures quoted so far relate to the relative wastages by aerial