The U. S. Pharmacopoeia directs this preparation to be made by macerating opium, nutmeg, and saffron in diluted acetic acid, and afterwards subjecting the mixture to percolation with the same menstruum, taking care that the strength shall be uniform by adding sufficient diluted acetic acid to make a certain volume. Some sugar is added previously to the diluted acid. The vinegar of opium was introduced as a substitute for the Lancaster or Quaker's black drop, and is believed to be preferable to opium in substance or tincture, in certain cases in which the two latter forms disagree with the stomach or nervous system. This modification of effect may be owing to the absence of certain principles of opium soluble in alcohol, but not in water, or to the change of the natural meconate of morphia and of the other alkaloids into the acetate, or to both these causes. It is much stronger than laudanum, and may be given, for its full anodyne and soporific effects, in the dose of from seven to ten drops.