376 HANDBOOK OF PHOTOGRAPHY 



p-Phenylenediamine 



Ethyl p-phenylenediamine 



Diethyl p-phenylenediamine 



Methyl p-phenj'lenediamine 



Dimethyl p-phenylenediamine 



These are sometimes supplied as the hydrochloride. 



The methyl compounds are toxic to most people, the mono-compounds frequently 

 give poor colors, as does the p-phenylenediamine itself leaving the diethyl p-phenyl- 

 enediamine, usually supplied as the hj^drochloride, as the most important agent for this 

 special field. When this is used as the color-forming developer, a large number of 

 compounds can be used to produce colors. A few are listed below: 



For yellows: 



Acetoacet-2,5-dichloranilide 



Acetoacetanilide 



Acetoacet-o-chloroanilide 



For magenta: 



p-Xitrophenylacetonitrile 

 l-Phenyl-3-methyl-5-pyrazolono 



For blue to blue-green : 



Alpha-naphthol 



o-Hydroxydiphenyl 



4-Chlorophenylphenol 



In case commercial use of color formers is contemplated, the patent situation 

 should be thoroughlj^ investigated, as many are covered bj^ patents, though the 

 patents expired some years ago on the compounds used in the earlier work in this field. 



Color can be produced by the direct development of the latent image, but the 

 reducers and formulas used are rather weak as developers; it is somewhat simpler to 

 develop and fix the emulsion as usual, then bleach and redevelop in the appropriate 

 formula. This redevelopment again deposits the silver image which must be removed 

 in turn by additional bleaching and fixation or equivalent steps. 



A typical procedure for producing a colored image in positive motion-picture film 

 for example is: 



1. Expose and develop as for any ordinary print. 



2. Rinse, fix, wash, and dry (if desired). 



3. Bleach to silver ferrocyanide in: 



Potassium ferricyanide 37 . o g. 5 oz. 



Ammonia (concentrated) 5 . cc. 5 fl. dr. 



Water to 1 1. 1 sal. 



4. Wash thoroughly 



5. Redevelop in: 



Diethyl p-phenylenediamine hydrochloride 3 g. 175 gr. 



Sodium sulphite (anhydrous) 5 g. 290 gr. 



Sodium carbonate (monohydrated) 35 g. 4 oz. 290 gr. 



Water to 11. . 1 sal. 



to which the following solution has been added just before use: 



Color former J-i-2 g. 15-120 gr. 



Alcohol 100 cc. 12K fl. oz. 



