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The viscosity of cholesterol dispersions in aqueous buffered surfactant solutions has been reported under progel conditions. The viscosity versus concentration curves pass through maximum which corresponds to the beginning of solubilization of cholesterol into the surfactant solutions. The stability of the dispersions has been explained by a mechanism involVing formation of association complex between cholesterol and the surfactants through hydrogen bonding.

The aqueous and alcoholic extract of Urena lobata flowers has been used in acid/alkali titrations over a wide range of concentration. The results obtained with the flower extracts have been compared with those obtained by using traditional chemical indicators like phenolphthalein and methyl orange. It has been established experimentally that the flower extract can be successfully used in place of phenolphthalein and methyl orange for acid/alkali titrations. The presence of anthocyanins is supposed to impart pH sensitive colour dependence to the natural indicator.

A BSTRA CT Adsorption of petroleum sulfonate TRS 10-80 on a mineral sand, characterized by chemical analysis and infrared spectra to be silica, has been studied under conditions relevant to the practical field. The adsorption is significantly affected by the age of the sulfonate solutions. A new mechanism of adsorption involving sulfonate monomers and multimers has been proposed. The adsorption behavior is best characterized by Langmuir and Freundlich models. At higher temperatures, the mineral surface seems to be capable of forming chemical bonds with the sulfonate anions. Micelles are not considered to be the species favored for adsorption. The adsorption, depending upon the concentration of added electrolyte, either reaches a saturation value or decreases abruptly after a fixed surfactant concentration has been reached. The apparent surfactant loss at higher salt concentrations seems to be due to salting-out of the sulfonate rather than its adsorption. NOMENCLATURE= Langmuir constant representing intensity of adsorption = depletion in surfactant concentration after adsorption = equilibrium surfactant concentration (wt%) b AC ce CMC = critical micelle concentration D = sulfonate dimer K

Adsorption of Triton X‐100 on a reservoir sand (characterised by chemical analysis and i.r. spectra to be silica) has been studied under field conditions. The adsorption behaviour is best characterised by Freundlich and Temkin adsorption models. The kinetics of adsorption is found to be very much dependent on temperature and the rate of adsorption shows an anti‐Arrhenius temperature dependence. The adsorption is proposed to proceed through Si—CH3 bond formation. Addition of common inorganic salts is found to cause maxima and minima in the adsorption isotherm and to change the shape of the isotherm.