At the moment of emulsification, when concentrations of silver nitrate and alkali halide solutions exceed certain critical values, coarse grains of silver halide (pepper) were formed, but the coarse grains disappear by standing with agitation in presence of excess halide and some kind of polymer (cf. fig. 1A). This phenomena called “ peptisation”.
On the other hand, in the presence of excess silver ions, peptizing effect does not appears with any polymer so that the peptizing effect for silver halide is caused by the excess halide ions.
The critical concentrations varies according to the kind of polymer, but this difference is little, compared to the difference of peptizing effect between various polymers. For examples, PVA and PAM begin to give coarse grains almost at the same ionic concentrations but after standing with PVA, coarse grains remain unpeptized, whereas PAM has very strong peptizing effect and gives finely divided grains even in very high ionic concentrations.
The difference of peptizing effect between various polymers is considered to be caused by the difference of the degree of aggregation by salt, therefore, aggregated polymer disturb the adsorption of halide ions on the silver halide crystals.
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