Reduction of solid silver salts

The reduction of silver chloride, precipitated in the presence of excess chloride ion, yielded the S-shaped curve typical of an autocatalyzed reaction (James, 25). The initial reaction rate, measured in terms of the reciprocal of the time required to complete 5 % of the total reaction, varied directly as the hydroxylamine concentration and inversely as the chloride ion concentration when the latter was relatively large. The specific surface of the freshly prepared precipitate, as measured by dye adsorption, decreased with aging, and the reaction rate decreased proportionately. 

The reaction rate was diminished by shaking the precipitate in a gelatin solution for some time prior to addition of the hydroxylamine. The rate decreased sharply as the amount of gelatin increased until a minimum rate was attained. Further addition of gelatin had no measurable effect. Gelatin also decreased the rate of reduction of silver ions 

The cyanine dye, 3,3 -diethyl-9-methylthiacarbocyanine chloride, had a much greater effect than gelatin in decreasing the reaction rate of the silver chloride. The rate of reduction of silver chloride varied linearly with the amount of silver chloride surface not covered by the dye, and the rate attained at complete coverage was of the order of one-thousandth that for the undyed precipitate. The dye exerted scarcely any effect upon the reduction of silver ions from silver sulfite complex solution. 

The kinetics of the silver-catalyzed reduction of silver chloride were studied on two types of preparations. In the first the nuclei were 

The reduction of nucleated precipitates varied directly as the 0.8 power of the hydroxylamine concentration and inversely as the 1.25 

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