Troy Weight is used for weighing gold, silver, and jewels, and in chemical experiments; and 4 grains of Gold are considered as making one carat, when we consider the fineness of gold. Articles of jewellery are marked according to the fineness of the gold," 20 carats fine" means that 20 parts out of 24 are pure gold; "18 carats fine," that 18 parts are pure gold, or; gold watch-cases, etc., are made of this fineness of gold. In coining gold, an alloy of 2 parts of copper to every 22 of gold is added to the metal to harden it, and rendering it capable of resisting the wear to which it may be subjected. Out of a pound Troy of standard gold about 46 sovereigns are coined. Perfectly pure gold is quite soft and soon rubs away. The price of gold 22 carats fine is generally £3, 17s. 10d., whilst the price of pure gold is £4, 4s. 11d. per ounce. The price of gold as quoted in the market is about £3, 17s. 94d. per ounce, owing to slight impurities being left in it after reduction.

Silver. To harden silver, the mint authorities mix 7 parts of copper to every 92 parts of pure silver, then they make a pound Troy into sixty-six shillings. Silver will generally fetch from 5s. to 5s. 6d. per ounce.

Bronze Coinage.-Out of every hundred parts, the bronze for coins consists of 95 parts of pure copper, to 4 of tin and 1 of zinc. A halfpenny is exactly 1 inch across, and three pennies weigh one ounce.

The 1 lb. Avoirdupois=7000 grains Troy.

Avoirdupois Weight.-All articles of commerce, and all necessaries of life, are weighed by Avoirdupois Weight, which is the common standard of weight. A pound Avoirdupois consists of 7000 grains, and a pound Troy of 5700. It must be borne in mind that an ounce Troy is heavier than an ounce Avoirdupois, or, if you like, that an ounce of gold is heavier than an ounce of feathers, and a pound of feathers is heavier than a pound of gold, but a pound of feathers is the same weight as a pound of iron.

Apothecaries' Weight is used by druggists and the medical profession when mixing their prescriptions, and weighing drugs and medicine; but they themselves buy by Avoirdupois Weight.

Cloth Measure is here given, but it is seldom now used, except in arithmetics to puzzle little boys and girls; but it is as well to remember that 16 nails make one yard.

Long Measure.—This with the Money Table and Avoirdupois Weight, form our most useful tables. By it all measures relating to length, breadth, heights, and distances are expressed.

Land, Square, or Superficial Measure.-By means of this table all quantities relating to surfaces are expressed, such as the surface of this sheet of paper, the area of the walls of the schoolroom, the size of a farm, the space occupied by a building or town.

Cubic or Solid Measure.-This measure is used to give the contents or bulk of objects; this bulk is calculated by multiplying the length, breadth, and thickness together. For instance, a cubic yard of coal is a block of coal measuring 3 feet long, 3 feet wide, and 3 feet high, hence its contents is 3×3×3=27 cubic feet; such a piece of coal would be called a cubic or solid yard.