Physical Development and the Reduction of Silver Ions from Solution

Physical Development and the Reduction of Silver Ions from Solution 

Sheppard s mechanism was formulated primarily in reference to direct development (Sheppard, 3 Sheppard and Meyer, 3a) and he assumed that the complex was formed in the act of or as a result of adsorption of the developing agent by the silver halide. Since he did not specifically suggest application of the basic mechanism to physical development, consideration of his mechanism will be deferred until direct development is treated in detail. 

James has investigated in some detail the kinetics of the reduction of silver ions by several developing agents. Without exception, the reduction was markedly catalyzed by metallic silver. 

The most extensive work on the catalyzed reaction was carried out with a nuclear gold sol (phosphorus reduction) added as the initial catalyst. The gold particles soon become coated with silver, so the major portion of the measured reaction is actually silver-catalyzed. The reaction rate is proportional to the surface area of the catalyst. This is shown by the following experimental results. 

For any particular silver ion and hydroquinone concentration, the rate is proportional to the amount of nuclear sol added. When reaction 

---

II. Physical Development and the Reduction of Silver Ions from Solution. 109... 

---