A study of the pharmacopoeial method for the preparation of solution of chloroxylenol.

Abstract

Summary In preparing routine batches of solution of chloroxylenol, a wide variation from batch to batch has been observed in the volume of oleic acid required to adjust the soap solution to the official end-point. Investigation has shown this to be due to the masking of the colour change of bromothymol blue in yellow solutions. The disappearance of the pink colour of phenolphthalein is more readily observed, and from a curve showing the relationship between the pH value and the volume of oleic acid added, it is possible to calculate what further volume is required to reach the official end-point, or for that matter any other desired point. During the course of the work, experimental evidence has been obtained to show that indicators do not provide a reliable guide to the pH value of soap solutions, and that solution of chloroxylenol may be much more alkaline than would be expected from the colour which it gives with bromothymol blue. A formula and method of preparation is given for a product of constant and reproducible composition, which is less alkaline than the official preparation, paler in colour, and less likely to darken on storage. Its bactericidal activity is not affected by the change.