Synthetic retarders having thiol radical, gave typical Langmuir isotherms in adsorption on photographic emulsions. Samples having no thiol grouping can be adsorbed, but the order of amount adsorbed is one tenth of the former. In spite of the difference of the adsorption properties, adsorbed amount necessary to retard the after-ripening process to the same order is almost equal. On some assumptions, area of domain encircled by adsorbed molecules was computed from experimental data. If the mechanism of chemical ripening by reduction is an autocatalytic one, this domain may represent sensitivity specks of maximum size in this experimental emulsion.
Estimation of this size gave the area of 700-2000 A
2, which is filled of 40-270 270 atoms of silver.
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