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.
Zinc sulphate is a good emetic for cases of this kind: 10 gr. in warm water is an average dose, but 20 gr. is the amount preferred by many practitioners; if the mouth be firmly closed, it may be administered by a tube passed through the nose to the gullet, or by the stomach-pump through a gag, and if the larger dose be used, its after-rejection must be secured. When an emetic is given by the stomach, its bulk has an effect in securing the result: thus, the greater quantity of warm water that can be given with the zinc sulphate the better it will act: time also makes a difference, for smaller doses given slowly have acted better than large ones quickly swallowed. In some cases a few grains have been given by intravenous injection, and have produced emesis.