In the British Empire the weights and measures most commonly employed for dispensing-purposes are those of the Imperial system and the old apothecaries' weights and measures. The unit of weight in each is the same-namely, the grain, an entirely arbitrary but exceedingly convenient unit. In the United States of America similar systems are in use, but the standards employed there are those originally introduced from England when the United States was a British Colony; and as many changes have since been made in our Imperial system, there are differences between the American and British standards, although the designations may be the same. The differences between the two systems are in measures and higher weight denominations than the grain, which is the same in both.

The United States standard for measure is the old wine-gallon, used in England before 1826; this gallon being 231 cubic inches in capacity. It is divided into 8 pints, each of 16 ounces; the ounce is divided into 480 minims, and a minim of pure water at 220 C. weighs 0.9483 grain.

The Imperial gallon is the measure, at 620 F. and normal pressure, of 10 pounds, or 70,000 grains, of pure water- that is, a volume of slightly over 277 1/4 cubic inches. It is divided into 8 pints, each of 20 ounces, the ounce being divided into 480 minims; and a minim of pure water at 62° F. weighs 0.9114 grain, so that 50 Imperial minims equal 48 American minims.

The Imperial ounce is 437 1/2 grains, but the American is 4557. The apothecaries'system is used in both countries, and the weights are the same-that is, one apothecaries'grain is equal to one avoirdupois grain in both, and the scruple equals 20 grains, the drachm equals 60 grains, and the ounce equals 480 grains-Americans generally speak of it as the 'Troy ounce,'Britishers saying the 'apothecaries'ounce'or 'Troy ounce'according to the trade in which it is used.

It is the custom in the British Empire and in the United States, when dispensing, to weigh solids and measure liquids, and that is the rule of this book.