Higuchi and Lach, "Investigation of Complexes Formed in Solution by Caffeine. VI. Comparison of Complexing Behaviors of Methylated Xanthines with p-Aminobenzoic Acid, Salicylic Acid, Acetylsalicylic Acid, and p-Hydroxybenzoic Acid,", 1954

Higuchi and Lach, "Investigation of Complexes Formed in Solution by Caffeine. VI. Comparison of Complexing Behaviors of Methylated Xanthines with p-Aminobenzoic Acid, Salicylic Acid, Acetylsalicylic Acid, and p-Hydroxybenzoic Acid,", 1954, Box: 10, Folder: 190. Personal papers of Takeru Higuchi, PP 359. University of Kansas. Kenneth Spencer Research Library. https://archives.lib.ku.edu/repositories/3/archival_objects/124614 Accessed February 16, 2026.