1 Hectogram = 3 ounces, 8-3/8 drams avoirdupois.

1 Decagram = 154.32 grains Troy.

1 Gram = 15.432 grains.

1 Decigram = 1.542 grain.

1 Centigram = 0.154 grain.

1 Milligram = 0.015 grain.

CHAPTER XIII

USEFUL INFORMATION FOR THE WORKSHOP

To find the circumference of a circle: Multiply the diameter by 3.1416.

To find the diameter of a circle: Multiply the circle by .31831.

To find the area of a circle: Multiply the square of the diameter by
.7854.

To find the area of a triangle: Multiply the base by one-half the
perpendicular height.

To find the surface of a ball: Multiply the square of the diameter by
3.1416.

To find the solidity of a sphere: Multiply the cube of the diameter by
.5236.

To find the cubic contents of a cone: Multiply the area of the base by
one-third the altitude.

Doubling the diameter of a pipe increases its capacity four times.

To find the pressure in pounds per square inch of a column of water:
Multiply the height of the column in feet by .434.

Standard Horse-power: The evaporation of 30 pounds of water per hour
from a feed water temperature of 1,000 degrees Fahrenheit into steam at
70 pounds gauge pressure.

To find the capacity of any tank in gallons: Square the diameter in
inches, multiply by the length, and then by .0034.

In making patterns for aluminum castings provision must be made for
shrinkage to a greater extent than with any other metal or alloy.

The toughness of aluminum can be increased by adding a small per cent.
of phosphorus.

All alloys of metals having mercury are called _amalgams_.

A sheet of zinc suspended in the water of a boiler will produce an
electrolytic action and prevent scaling to a considerable extent.

Hydrofluoric acid will not affect a pure diamond, but will dissolve all
imitations.

A strong solution of alum put into glue will make it insoluble in water.

A grindstone with one side harder than the other can have its flinty
side softened by immersing that part in boiled linseed oil.

One barrel contains 3-3/4 cubic feet.

One cubic yard contains 7-1/4 barrels.

To find the speed of a driven pulley of a given diameter: Multiply the
diameter of the driving pulley by its speed or number of revolutions.
Divide this by the diameter of the driven pulley. The result will be the
number of revolutions of the driven pulley.

To find the diam