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666 LEVENSON December
Elon by hydroquinone. The course of oxidation by oxygen (autoxidation) is similar to that of oxidation by silver bromide, and a similar mechanism may be assumed.
I. SYSTEMS OF DEVELOPER AGITATION
Because the rate at which oxygen attacks developers is appreciable* it is customary to protect them from exposure to the atmosphere as much as possible. However, in order to achieve uniformity of treatment of the film that is being developed, it is necessary to introduce considerable turbulence in the developer solution so as to change as frequently as possible the developer actually in contact with the sensitive emulsion. Mere circulation of the developer is not usually adequate to achieve this end and systems have been described, for example, in which the developer is projected at the surface of the film from submerged jets.
On the other hand, there has teen a tendency in recent years to achieve the desired degree of agitation by methods that involve the free exposure of the developer to air. Machines have been described in which the developer is cascaded down the strands of film from a trough situated above the racks. Ives and Kunz,3 and Crabtree and Schwingel4 have shown that a developer can be suitably agitated by means of bubbles of air released from submerged jets and that, in spite of the aeration, the sensitometric properties of the developer can be maintained constant by proper replenishment.
Spray Development
The latest move in this direction has been to abandon altogether the idea of immersing the film in a tank of developer and, instead, to apply the developer to the loops of film by spraying it on in mid-air. Several machines based upon this principle are in use in the United States and at the time of writing this paper, similar machines are coming into use in the United Kingdom.
In these machines the degree of aeration is extreme and, at first sight, one might suppose that the rate of loss of chemicals by aerial oxidation would be too severe for the idea to be practical. While it is generally understood in the industry that the chemical consumption is increased only slightly, if at all, no comparative figures have been published. To gain a closer insight into the economics of this method of processing, a study was made to compare the performance of a pilot