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366 HISTORY OF COLOR PHOTOGRAPHY
3. i-p-chlor-phenyl-3-methyl-4-amino-5-pyrazolone 5.0 parts
Sodium sulphite 5.0 parts
Potassium bromide 0.5 part
Water to 1000 parts
The last two solutions yield yellow dye images together with the silver. Ortho-amino phenol has the structure
-OH
therefore it is a good developer, and capable of yielding dye images. It would appear that this compound and its substitution products are covered in the patent above, but the I.G. made doubly sure by another patent (Eng. P. 457326), issued a short time before the one discussed above. Yellow to red images are obtained. Typical examples are the following:
Yellow dye image
4: 5-di-methyl-2-methyl amino-phenol i.o part
Sodium hydroxide 0.8 part
Water to 200 parts
Orange image
2 -methyl amino-phenol i part
Potassium carbonate 10 parts
Water to 200 parts
Red image
4-chloro 2 -methyl amino-phenol 2 parts
Potassium carbonate 15 parts
Water to 200 parts
A further extension was made by the I.G. (Eng. P. 482652), when it disclosed that developers like pyrogallic acid, ortho-amino-phenol, etc., could be made into primary color developers by substituting a heavy residue into the molecule. Suitable for this purpose are groups such as diphenyl, stilbene, azoxybenzene, 2 : 3-oxy-naphthoic acid, diarylureas, benzthiazol, etc.
In 1936 and 1937 Karl and Ludwig Schinzel wrote a series of papers in the magazine Das Lichtbild (Vols. n and 12). In the first of these articles, the chemistry of primary color development is discussed (Vol. n (1936), p. 172; Phot. Ind.y Vol. 34 (1936), p. 942). The application of these findings has been protected by Karl Schinzel in a series of disclosures assigned to the Eastman Kodak Company (Eng. P. 498869, 498870, 498871, and 498875). They found that hydroquinone, and naphth-hydroquinone can yield color images directly if heavy substitutions are placed within the molecule. Lemonyellow images can be obtained if 2 : 5-diaryl-, 2 : 5-di-phenoxy-, 2 : 5-diphenetylhydroquinone, or 2-phenyl-i : 4-dioxy-naphthalene be used as the developing agent.