Crystalline KF reacts with solid acidic substances by milling in an agate mortar. Proton transfer takes place between the acid and KF with formation of KHF2 and the K salt of the acid. The reactions were monitored by IR and XRD techniques in the solid reaction mixture. The following substances react readily with KF : KHSO4, KH2O4, (NH4)(2)SO4, and organic acids (oxalic, maleic, benzoic, p-chlorobenzoic, p-nitrobenzoic, miristic and nicotinic). NH4F, NaF are less reactive in that order while LiF and CaF2 are inert.