Abstract
Aqueous solutions of gentisic acid, adjusted to a pH between 5.0 and 8.0, exhibit maximum absorption at 320 mμ, the absorbancy being proportional to concentration at least to 3 5 mg./L. Solutions of salicylic acid, adjusted within the same pH range, exhibit maximum absorption at 296 mμ, the absorbancy likewise being proportional to concentration. At 306.5 mμ, the isobestic point, both gentisic acid and salicylic acid have the same absorbancy in solutions of identical weight concentration. From readings of the absorbancy at 296 and 320 mμ of an aqueous solution containing gentisic and salicylic acids, adjusted to a pH between 5.0 and 8.0, the amount of eafh acid present in the solution may be calculated by means of simultaneous equations. The determination of the absorbancy at 306.5 mμ may be used to confirm the total amount of acids present.
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