This section is from the book "Materia Medica And Therapeutics Inorganic Substances", by Charles D. F. Phillips. Also available from Amazon: Materia medica and therapeutics.
In the chronic stages of this complaint, where secretion is profuse and spasm severe, and there is not much complicating bronchitis or pyrexia, I have seen alum exert a very beneficial influence: 4 to 10 gr. in water or syrup should be given three or four times daily. Dr. Golding Bird introduced and highly commended this treatment, conjoining the alum with conium and dill-water. Dr. Meigs states that alum has given him, in sixty-eight cases, better results than any other remedy (Diseases of Children). Its good effect may be traced, probably, to a local astringent action on the fauces; hence it is best administered in some thick vehicle, and swallowed slowly.