We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
May, 1938] MQ DEVELOPER 563
The latent image curves are particularly interesting. The latent image does not start to develop at the equivalence point, but 60-70 millivolts to the left of it, which means that a stronger developer is necessary to develop an exposed halide grain that has not been partially developed, than one that has been partially developed. It is thus seen that the lower limit of potential that a compound must have, to be a developer, is really a little different from that mentioned previously. It is hardly necessary to say that this is a sufficient condition to make a developer, but the actual value is different for every compound and depends upon the exposure.
As was mentioned before, there has been some question about the possibility of measuring the reduction potentials of organic developers. About two years ago Evans and Bahler in the Kodak Research Laboratories found that when a platinum electrode was immersed in a mixed developer a definite and repeatable potential was set up. It was not thought that this was the true electrochemical reduction potential of the system but was probably somewhat closely related to it. However, it was a very interesting variable, and considerable work was done in order to determine just what relation it did have to the true reduction potential of the system. The complete technic of measuring this potential and some experimental data obtained by its use were published in April, 1937. 2
The work of Reinders and Beukers was repeated but using organic developers, and static potentials were measured by the new technic. Fig. 2 is taken from this paper and is exactly similar to that reproduced from Beukers' thesis except that amidol was the developing agent. In this case the potential measurements were made using a saturated calomel electrode as the standard, rather than the hydrogen electrode. (As mentioned before, this electrode has a potential of +0.250 volt against the hydrogen electrode.) All the pH measurements have been made with a glass electrode, and sodium ion errors have been partially neglected. (Note: It is probable that the sodium sulfite in these solutions had been used up by aerial oxidation by the end of the reaction.)
On converting these potentials to the hydrogen system it is seen that the equivalence point checks with that obtained by Beukers within 10 millivolts. This would appear to indicate that the potentials as measured are the true reduction potentials of the solutions, but until further evidence is obtained it is best to refer to them merely as the "measured potentials."