Lead nitrate crystals, adsorption

The concept that selective adsorption can be caused by qualitative characteristics of the surface is supported by studies of adsorption on plane surfaces Lead nitrate crystals adsorb Methylene Blue on the 110 faces, whereas a different set of faces does not adsorb this dye but will adsorb picric acid. When placed in a solution containing both dyes, lead nitrate crystals will develop a blue color on one set of faces and a.yellow color on others.32... 

There is nothing new in principle about the use of isotopes as an aid to chemistry. For twenty years the radioactive elements have been used as indicators to study adsorption, solubility, volatility, distribution, and other phenomena of physical chemistry. Distribution of heavy radioactive atoms in plants has been studied through the relative amount of ionization found in the different parts. The ionization theory was supported by dissolving radioactive lead chloride in an aqueous solution of ordinary lead nitrate and then crystallizing out the lead chloride. The radioactive lead was found to be equally distributed between the two salts. In aqueous solution the two different kinds of lead are free to exchange anions, as predicted from the electrolytic dissociation theory. With un-ionized compounds of lead it was found that exchange does not take place. 

Studies with crystals indicate that the specificity, so often encountered in adsorption, can depend on mutual relations between the lattice structure of the solid and the configuration of the adsorbed substance. Methylene Blue is adsorbed by crystals of lead nitrate, but not by potassium sulfate. Nellensteyn1 found that diamond powder adsorbs Methylene Blue but not succinic acid, whereas graphite adsorbs succinic acid but not Methylene Blue. 

Numerous studies made by France10 and his coworkers lead to the conclusion that the adsorption of a given dye by a growing crystal is a specific process, depending on the structure of the crystal as well as on the shape, presence, and position of polar groups in the dye molecule. Adsorption may occur when only one substituent group of the dye can fit into the ionic planes of a crystal face. France and Wolfe,10 in a study of the adsorption of thirty isomeric monoazo dyes by crystals of sodium nitrate, sodium bromate, and sodium chlorate, found twenty-five of the dyes to be adsorbed by sodium bromate, six by sodium nitrate, and two by sodium chlorate. Although each of the dyes was adsorbed on at least one type of crystal, only one of the thirty dyes was adsorbed by all three crystals. 

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