Silver chloride emulsions prepared with polyvinyl alcohol as protective colloid consist of very fine grains not exceeding 0.05 micron in diameter which scarcely grow by long ripening at high temperature. Addition of a small amount of the compounds known as sulphurcontaining sensitizers, e. g. thiosinamine, thiosulphate or rhodanine to this emulsion starts abrupt growth of grains which can be followed by nephelometry. Using this technique, the action of various substances as “anti-retarders” or “physical ripening accelerators” is investigated. Turbidity increase is plotted against the concentration of the addition (on a logarithmic scale) using ripening time as parameter, characteristic curves for various substances are obtained. From these the comparison of their activities is possible. A small addition of gelatin also produces an increase of grain-size and turbidity, and characteristic curves of various gelatin thus obtained are very particular as regards types of gelatins., e. g. inert, semi-inert, active or retardative etc., so they, are useful for classifications and estimations of their photographic properties. The properties of substitution products of above mentioned artificial sulphur-containing sensitizers with aliphatic long chain radicals closely resemble those of natural active substances. This confirms the author's hypothesis that the active substance in gelatin must have a high-molecular constitution or at least be a very large molecule.