Osmotic Properties of Aqueous Solutions Containing Caffeine

Abstract

An improved form of the thermoelectric osmometer developed by one of the authors has been used to study solutions of p-aminobenzoic acid, citric acid, sodium citrate, sodium salicylate, sodium benzoate, morphine hydrochloride, and papaverine hydrochloride alone and in combination with caffeine. The measured colligative property is plotted against concentration of caffeine. These data are described by two intersecting straight lines for each substance. The point of intersection occurs at different positions on the caffeine scale depending upon the nature and concentration of the complexing agent. The shift along the caffeine scale from the break in the pure caffeine data is divided by the concentration of the complexing agent to give a characteristic complexing capacity number. Osmotic coefficients may be calculated from tabulated slopes. An improved form of the thermoelectric osmometer developed by one of the authors has been used to study solutions of p-aminobenzoic acid, citric acid, sodium citrate, sodium salicylate, sodium benzoate, morphine hydrochloride, and papaverine hydrochloride alone and in combination with caffeine. The measured colligative property is plotted against concentration of caffeine. These data are described by two intersecting straight lines for each substance. The point of intersection occurs at different positions on the caffeine scale depending upon the nature and concentration of the complexing agent. The shift along the caffeine scale from the break in the pure caffeine data is divided by the concentration of the complexing agent to give a characteristic complexing capacity number. Osmotic coefficients may be calculated from tabulated slopes.