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. Although commonly described as a Wh~~=:m• stainless developer, an oxidized or stale hydroquinone solution will produce yellow stains, as in the prolonged forcing of an underexposed negative in development (wherein hydroquinone should not be used.). This stain rarely yields to ordinary "clearing" agents, but may be removed by the skilful use of Farmer's Reducer, the process of stain-removal being carefully watched so that the density of the negative is not affected. . Thus far we have considered the use Combined With of hydroquinone alone as a developer Other • hih . h .. • Developer• m w c use Its c aractenstics are most dearly exhibited. By far its largest use, however, is in combination with other developers, such as metol, paramidophenol, edinol, rodinal, etc. Its action in all these combinations seems to be to add vigor and density-giving power. Formulas for such combinations are given in the consideration of the respective developers mentioned. Pyroeatechin Identical in chemical composition -oH with hydroquinone, but differing from -oH it in constitution, in that the two dioxy groups (OH)z are substituted for () the hydrogen atoms in the ortho position in the benzene ring, we have pyrocatechin or catechol. This is known to chemists as ortho-dioxy-benzene, CeH4 (OH). and comes in prismatic colorless crystals, freely soluble ·in water and alcohol. The use of alkaline solutions of Hiatory: Variations pyrocatechin for development was observed by Eder and Toth in t88o, but it comes within our survey of modern developers because of its re-introduction in 1898, in modified forms, known as Elconal, Elconal F and Kachin. These seem to have disappeared from the market, but pyrocatechin is still listed by a few chemists. C d "th In action pyrocatechin is said to be B':Z~~in-:e more e!lergetic t~a~ hydroquinone, .b~t otherWise very Similar except that It IS not so markedly influenced by ordinary variations of

Modern Photographic Developers  
Modern Photographic Developers  

A Practical Handbook to the New Developers Telling What They Are and How to Use Them with Reliable Formulae by The Photo Miniature, January...