Alkalis developing agents

The requirements of a developer moiety for incorporation into a dye developer are well fulfilled by hydroquinones. Under neutral or acidic conditions hydroquinones are very weak reducing agents and the weakly acidic phenoHc groups confer tittle solubility. In alkali, however, hydroquinones are readily soluble, powerful developing agents. Dye developers containing hydroquinone moieties have solubility and redox characteristics in alkali related to those of the parent compounds. 

Dye release may relate either directly or inversely to the image-related reduction of silver halide. Release of the dye or dye precursor may be accomphshed or initiated by the oxidized developing agent or the unoxidized developing agent or by alkali or silver salts. 

Also, the higher the pH, the faster a developer will oxidize. To prevent oxidation, developers often are stored in separate A and B solutions that are mixed just prior to use. Developers using caustic alkali should always be formulated in this manner. Developers containing easily oxidized developing agents, such as pyro, should also be stored this way, regardless of which accelerator is used. 

Technique of Divided Development In divided development, two separate baths are used. The first bath contains the developing agent(s), restrainer, and preservative. The second bath contains the accelerator. The second bath is used to activate the developer. Borax is the least active accelerator metaborate is about double the strength of borax carbonate is about double the strength of metaborate. Hydroxide is the most active of the alkalis and the least controllable. 

Uses As a developing agent used in conjunction with sodium or potassium carbonates or with caustic alkali. The sodium salt of this is the developing agent in the concentrated solution of prepared developer. It is marketed under the trade name of Rodinal by Agfa. 

Uses High-energy accelerator or alkali sometimes used to activate low-energy developing agents (e.g., hydroquinone). 

Uses As an ecologically friendly developing agent, usually in combination with metol or Phenidone. It can also be used as a substitute for hydroquinone. Start with 1.8 times the weight of the hydroquinone. Sodium isoascorbate is not acidic so the alkali does not have to be increased. 

None of the paper developers in this section is written in stone. Many of them were created by photographers, not unlike you, who were experimenting with various proportions of developing agents and alkali. Feel free to alter any of the formulas. If your new brew gives you the tone/color, look, and feel you re after, great. If not, you may lose a few sheets of paper. 

Developers containing a high sulfite and low alkali concentration, such as Kodak D-76 and ID-11, should not be used for redevelopment because the sulfite tends to dissolve the silver image before the developing agents have had time to act upon it. 

The oxidation of the compounds used as developers is accelerated in the presence of alkalies and retarded by acids for this reason most developers are made up just before use from two solutions, one containing the developing agent, and the other sodium carbonate. 

The developing agents used for chromogenic development are generally members of the p-phenylenediamine class. Quinonediimines formed by oxidation of the developer react with the couplers, which are often precursors of indophenol or azomethine dyes. Although removal of the oxidation products of the developer by sulfite is not desired in chromogenic development, a little sulfite is usually still added to protect the developer from oxidation by air. As in b/w development, alkali and antifoggant materials are also present. 

Reactor-grade zirconium is essentially free of hafnium. Zircaloy(R) is an important alloy developed specifically for nuclear applications. Zirconium is exceptionally resistant to corrosion by many common acids and alkalis, by sea water, and by other agents. Alloyed with zinc, zirconium becomes magnetic at temperatures below 35oK. 

Chemical Reactivity - Reactivity with Water No reaction Reactivity with Common Materials Attacks copper and copper alloys these metals should not be used. Penetrates leather, so contaminated leather shoes and gloves should be destroyed. Attacks aluminum in high concentrations Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization May occur spontaneously in absence of oxygen or on exposure to visible light or excessive heat, violently in the presence of alkali. Pure ACN is subject to polymerization with rapid pressure development. The commercial product is inhibited and not subject to this reaction Inhibitor of Polymerization Methylhydroquinone (35 - 45 ppm). 

Solutions of alkali metals in liquid ammonia have been developed as versatile reducing agents which effect reactions with organic compounds that are otherwise difficult or impossible/ Aromatic systems are reduced smoothly to cyclic mono- or di-olefins and alkynes are reduced stereospecifically to frani-alkenes (in contrast to Pd/H2 which gives cA-alkenes). 

There are important developments to be expected in the commercial production of PM. As noted above, this enzyme proved to be a useful demethylating agent in the production of low-ester pectins. The use of enzymes has certain advantages over acid or alkali, and this fact might eventually create considerable market for PM preparations that are free or essentially free of PG. 

---