This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
"Most tinctures of the United States Pharmacopoeia are prepared with diluted alcohol, of the British Pharmacopoeia with proof spirit, and of the French and German Pharmacopoeias with alcohol of about 60 per cent., or of specific gravities 0.912 and 0.894. While it is desirable to keep the alcoholic strength of tinctures as low as possible, it is evidently improbable that one'and the same menstruum should be equally adapted for the preservation of liquid preparations of drugs having the most varied composition; and that improvements in this respect are needed, is shown by the unsightly deposits occurring in some, and the change into gelatinous masses observed in other tinctures. In most cases these obvious changes are prevented by the employment of a stronger alcoholic menstruum".