History of color photography (1945)

132 HISTORY OF COLOR PHOTOGRAPHY First, by the inclusion of the i8-carbon chain stearoyl residue; second, by the inclusion of a sulphonic acid radical; and third, by the substitution within the pyrazolone molecule of an amino-phenyl group. The coupling properties of this last group are destroyed by masking the amine group with the stearoyl residue. The blue-sensitive layer contains the sodium salt of meta-stearoylamino-benzoyl-acetanilide-para'-carboxylic acid. The molecule is made substantive first by the inclusion of the very heavy stearoyl residue, second by the inclusion of the acid carboxyl group which would allow the formation of a gelatin-carboxylate salt, and third by the presence of an amino-benzoyl group whose coupler properties have been masked when the amine group has been converted into a stearoyl-amide. It is to be noted that besides containing specific groups which yield substantive character, the molecules are all very heavy ones so that even if conditions are formed which would prevent their union with the gelatin, they would have a very limited range about which they could roam in the time during which they are sufficiently wet to be subject to diffusion. The cyan coupler present in the red-sensitive layer has a molecular weight of 613. The magenta coupler in the green-sensitive layer has a molecular weight of 543, while the yellow coupler present in the third layer has a molecular weight of 582. These are really giant molecules, which could hardly exist in solution except in colloidal state. Despite all the efforts which have been made to find new agents which would yield color-coupled dyes, it is interesting to note that all the cyan dyes are formed either from the hydroxy benzenes, or from the hydroxy naphthalines. This is true not only of all the coupling agents disclosed by Ansco and the I.G., but also of those disclosed by the members of the Eastman Kodak staff. And in the very early descriptions of Fischer and Siegrist, these substances were used for the formation of the cyan image. All that has been done in the generation that has passed since that time, is to tack on certain side-chain substitutions into the molecule. And Fischer and Siegrist outlined in some detail what the effect of substitutions .would be. The magenta couplers fall into two classes. First there is pyrazolone and the pyrazolone derivatives. These couplers appear to be preferred by Ansco and the I.G. Then there is benzyl cyanide and its derivatives. These appear to be favored by Eastman. The yellows, without exception, are all compounds which contain the central grouping — CO — CH2 — CO—. The only difference between the very many compounds that have been proposed, is in the nature of the groups which round out the molecule. Two such groups are needed to form the compound, and these can be anything from a simple hydrocarbon to a complicated substitution. After exposure, the pack is developed for fifteen minutes in an amidol depthdeveloper. Amidol 5 parts Sodium sulphite 50 parts Potassium bromide i part Water to 1000 parts