mas not investigated, since oxidation of the developer would interfere with the analysis. Evidently silver ions are, however, not necessary to effect the adsorption of the p-phenylenediamines and Elon. Levenson and James8-11 state that developers containing amino groups are able to be adsorbed by silver bromide because of their ability to form a covalent coniples with silver ion. Of the five developers studied, those that are adsorbed by silver do contain amino groups. The ability of the amino nitrogen to form a covalent complex with silver ion, and thus to promote adsorption by silver halide, is indicative of a property of the amino group which may or may not also be responsible for the adsorption of these developers by silver in the absence of silver ion. 'The heat of adsorption for I and I1 is too large for the adsorptive forces to be of the van der Waals type, and shows that some type of strong interaction between developer and metallic silver occurs. It is believed that the 3-methyl group on the I and I1 molecules16 increases the electron-releasing ability of the free amino group and this electromeric effect may contribute to the adsorptive forces. The weaker adsorption of simple p-phenylenediamine may be due to its symmetrical structure which causes a uniform distribution of charge over the molecule. Elon had a very weak adsorption which would be expected from an N-suhstitutet3-p-aminophenol. Hydroquinone, having no amino groups, is not adsorbed. In studying the rate of reduction of silver ions b y (16) R I.. Bent, et al., J .
A m . Chem. Soc., 73,3100 (1951).
hydroquinone and p-phenylenediamine in alkaline solution, ,James9statcs that the rate of reaction for hydroquinone is proportional to a fractional power of the silver-ion concentration. For p-phenylenediamine, however, the rate of reaction is dependent on the developer concentration to a fractional power. This is alw very strong evidence that silver-ion adsorption is necessary for hydroquinone to act a~ a reducing agent, while p-phenylenediamines may be adsorbed without silver ion on the surface. In studying postfixation physical development, Pontius and Thoinpson17 found, in the case of I, that the rate was proportional to the developed silver to the '/* power. This is consistent with ,James's postulates. Other give similar theories involving non-adsorption of black-andwhite developers and adsorption of p-phenylenediamine by silver. These measurements of adsorption of developers by qilver therefore confirm the evidence derived from the study of the kinetics of physical development. The method used for these measurements readily can be adapted to measurement of adsorption of other substances. Acknowledgment.-11-e wish to acknowledge the ~ror.1~ of Mr. A. Miller for the construction of the special qilica flow cell, and our indebtednes:, to Dr.. IY. R Riiby for many helpful discussions. (17) R. B. Pontius a n d J o a n S. Thompson, Phot. Set. E n g . , 1, 15 (1957). (18) T.H. James, J . Chem. Ed., 23, 595 ( 1 9 S ) (19) T. H. James a n d JY. Vanseloa, P h o t . Enganeerang, 6, 183 (1925).
T H E K ~ I O D T S A ~ I I PROPEIITIES C OF HIGHER FLUORIDES. I. THE H E i T CAPACITY, ENTROPY, ASD HEATS OF TlLlSSITIOS OF MOLTBDESURI HEXAFLUORIDE AND SIOBIUJI: PI?ST.IFI,T~ORIIDE1 BY A . P.BRADY, 0.E. A f Y E R S A N D I
