Troy Weight is used by jewellers and at the Mint. Its denominations are the pound, lb., = 12 ounces = 5,760 grains; ounce, oz., = 480 grains; and pennyweight, dwt., = 24 grains.
Apothecaries' Weight is used in prescribing and dispensing medicines, and in chemical and pharmaceutical operations generally. It is the official standard of the U. S. Pharmacopoeia. The British Pharmacopoeia uses the avoirdupois pound and ounce; hence the two agree only in the grain measure. The denominations of apothecaries' weight are the pound, lb, = 12 ounces = 5,760 grains; the ounce, oj, = 8 drachms = 480 grains; the drachm, dj, = 3 scruples = 60 grains; the scruple, sj, = 20 grains; and the grain, gr.
Avoirdupois Weight is the commercial weight, and is generally employed in the receipts in this volume. Its pound, lb., = 16 ounces, oz., = 7,000 grains. The ounce contains 437.5 grains. The apothecaries' or troy ounce contains 42 1/2 grains more than the avoirdupois ounce, and the apothecaries or troy pound contains 1.240 grains less than the commercial or avoirdupois pound. The troy pound contains 12 oz., the avoirdupois 16 oz.
_RELATIVE VALUE OF TROY AND AVOIRDUPOIS WEIGHTS._
Useful in determining the troy weight of silver by ordinary weights.
1 lb. troy = 0.822857 lb. av. = 13 oz. 72.5 grs.
1 lb. avoirdupois = 1.215277 lb. troy = 1 lb. 2 oz. 280 grs.
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