1958 年 78 巻 4 号 p. 319-321
It has already been revealed that tannin in crude drugs could be determined by the utilization of the fact that tannic acid undergoes reaction with methylene blue to form water-insoluble product (D-fying of methylene blue) in capillary analysis. The important point in this principle is that the reaction of tannic acid and methylene blue should be quantitative. In order to clarify this point, studies were carried out on the reaction of methylene blue with gallic acid, a componental part of the tannic acid molecule and which is considered to be responsible for its reaction with methylene blue. It was found that the phenolic hydroxyls in the gallic acid were responsible for the reaction of gallic acid and methylene blue, and that the molar ratio of the reaction was 1:1, by preparing capillary image and by determination of sulfur in the reaction product.