Ray's New Higher Arithmetic · Arts. 185–190 · Unit 11: Compound Denominate Numbers
48. Measures of weight
Goal: Your student knows which things were weighed by troy, apothecaries' and avoirdupois weight, and uses each table.
You'll need
- The book
- A slate, small whiteboard or scrap paper
- A notebook and pencil
What's in the book
Weight defined; troy weight (grains, pennyweights, ounces, pounds), apothecaries' weight (grains, scruples, drams, ounces, pounds), avoirdupois weight (ounces, pounds, hundredweights, tons), a comparison of the three, old British weights, and diamond weight.
The lesson, step by step
Warm-up
Ask: Which is heavier, a pound of feathers or a pound of gold? (In the old system, the pound of feathers! Keep reading.)
Weight
Read:
Weight is the measure of the force called gravity, which draws bodies toward the center of the earth.
Three kinds of weight are in use
Troy and apothecaries'
Read:
Troy Weight is used in weighing gold, silver, platinum, and jewels.
Table: 24 grains = 1 pennyweight, 20 pwt. = 1 ounce, 12 oz. = 1 pound.
Apothecaries' Weight is used by physicians and apothecaries in prescribing and mixing dry medicines.
It uses the same grain, ounce and pound, with scruples and drams in between.
Avoirdupois
Read:
Avoirdupois or Commercial Weight is used for weighing all ordinary articles.
Table: 16 oz. = 1 lb., 100 lb. = 1 cwt. (hundredweight), 20 cwt. = 1 ton.
Comparison
Read:
The pound Avoirdupois weighs 7,000 grains Troy
The troy pound is 5760 grains. So a pound of feathers (avoirdupois) is heavier than a pound of gold (troy). But an ounce of gold (480 grains) is heavier than an ounce of feathers (437½ grains).
Practice
Your student finds: grains in 2 lb. troy; pounds in 3½ tons; how many troy ounces are in an avoirdupois pound.
Wrap-up
The book also notes the British long ton of 2240 lb. used for coal and iron. Ask: Which ton is used in the U. S. table? (2000 lb.)
Tip
Troy ounces are still used for gold and silver prices today.
Answers to the book's problems
Practice: 2 lb. troy = 11520 grains; 3½ tons = 7000 lb.; 1 lb. avoirdupois = 7000 ÷ 480 = 14 7/12 troy ounces.
Worked out for this site from the scan. If a number in your copy differs, trust the book.