A modified apparatus as well as a procedure for the determination of methoxyl group was described.The main features were as follows: A reservoir with a siphon tube (B₁) or a cock (Bz) was used,and the reaction solution was heated vigorously and made to circulate quickly so that the time required for the determination could be shortened.For instance,by Pregl's method the reaction of papaverine hydrochloride required 90 minutes,while by this procedure it required only 15 minutes.Usually it takes only 10 minutes for one determination.The results obrained were satisfactory.