The pennyweight is the 1-240 part of the troy pound. Some 18 different values are recorded, varying from 7.42 grams to 24 United States grains, The troy ounce is the highest troy de nomination permitted in England, and is used in stating quantities of silver and other precious metals. In assaying the troy ounce is fre quently divided decimally. The silk troy ounce according to Troemner is the 1/16 of the troy pound and contains 360 grains. One hun dred and seventy-five troy ounces equal about 192 avoirdupois ounces.
The units of apothecaries' weights are as follows: One apothecaries' pound = 12 ounces =% drams = 288 scruples = 5,760 grains. The apothecaries' pound is equivalent to the troy pound in the United States, but in Eng land the apothecaries' weights based on the troy pound were discontinued in 1858 und, r authority of the medical act, and avoirdupois weights substituted in dispensing medicines. In the United States, the avoirdupois system is largely used in buying and selling drugs, al though the metric system is rapidly coming into use and displacing the apothecaries' on account of its great convenience. The apothe caries' grain is used in compounding prrs,rip tions of the more powerful drugs. The United
States apothecaries' scruple (20 grains) and the United States apothecaries dram (60 grains) are still used in compounding prescrip tions. The United States apothecaries' ounce (480 grains) is equal to the troy ounce. The apothecaries' pound (equal to the troy pound) is rarely used The units used in the weighing of diamonds are as follows: One diamond carat=4 dia mond grains=64 parts. The carat is the jew elers' unit for weighing diamonds, the name referring to a small hard bean formerly used for that purpose. In view of the variation in the value of the carat in different countries, its weight was fixed by agreement of London, Paris and Amsterdam jewelers, in 1878, at ex actly 205 milligrams. The following varieties of carats should he carefully distinguished: The international diamond carat of 205 milli grams, a definite unit free from ambiguity; the English diamond carat (3.2 troy grains or four diamond grains) differing, however, in different countries; the old carat (1-24 troy ounce); the gold carat (about 150 troy grains); and the gold carat, a ratio equal to 1-24 part by weight used in designating the purity of gold alloys. See also BALANCE; TONNAGE; WEIGH ING MACHINES.