The article by T. C. McILVAINE describes a buffer solution system that uses 0.2 M disodium phosphate and 0.1 M citric acid to cover a pH range from 2.2 to 8.0, suitable for arable soils and physiological media. The disodium phosphate was recrystallized and standardized by titration against HCl, while the citric acid was also recrystallized. The pH values of the mixtures were determined electrometrically using a specific cell configuration. A graph was constructed to determine the volumes of the two solutions needed to achieve any desired pH, with variations in observed pH values being less than 0.01. The titration curve for the phosphate-citric acid system is presented, showing its suitability for colorimetric pH determinations.The article by T. C. McILVAINE describes a buffer solution system that uses 0.2 M disodium phosphate and 0.1 M citric acid to cover a pH range from 2.2 to 8.0, suitable for arable soils and physiological media. The disodium phosphate was recrystallized and standardized by titration against HCl, while the citric acid was also recrystallized. The pH values of the mixtures were determined electrometrically using a specific cell configuration. A graph was constructed to determine the volumes of the two solutions needed to achieve any desired pH, with variations in observed pH values being less than 0.01. The titration curve for the phosphate-citric acid system is presented, showing its suitability for colorimetric pH determinations.