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Abstract
A comparison was made of the adsorption of four cyanine dyes from water and from ethanol by suspensions of silver bromide and silver iodide whose surface areas had been measured by gas adsorption. The effect of gelatin was examined and the adsorption by silver bromide suspensions and by photographic emulsions whose surface areas were obtained from electron-micrographs, was compared. It is shown that the surface of dry silver halide powder is unstable and that changes occurring on heating may produce considerable errors in surface area measurements by gas adsorption.
Under conditions where the surface was saturated with dye the average molecular areas of the adsorbed molecules varied over a wide range depending on the dye end the solvent and could not be accounted for in terms of simple stacking arrangements. The average molecular area of 3.3' diethyl-9-methyl thiacarhocyanine adsorbed from water both onto AgBr and Agl and also adsorbed from gelatin solution onto an iodobromide emulsion was found to be between 35 and 44A2 corresponding to more than one layer of dye adsorbed edge-on. These results cannot be reconciled with some previous published work. Adsorption from ethanol was only about one-third as great as from water.