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.
Prepare a solution as follows: take salicylic acid, one ounce; alcohol, five ounces. Of this solution add from two to five drachms to each gallon of syrup. If one ounce of syrup is used to every half-pint bottle, the proportion is for every bottle one to three grains of this solution, or from one-fifth to about one-half grain salicylic acid - a quantity infinitesimally small, and not likely to cause any harm, even if taken repeatedly and continuously; at least, experiments with healthy persons have proved this, but we are at a loss to report how it becomes the sick. It has been found that a solution containing one-fiftieth per cent, of salicylic acid - that is 0.2 gram per litre (quart) of water - very rapidly destroyed bacillus, and that yeast does not exert its fermentative faculties in presence of even a very weak solution of the acid. But just on this action may consequently be based the ground, that salicylic acid in the food of persons with weak digestions is injurious; as to those with strong digestive powers, if taken constantly with food, we decline to express an opinion.