20” X 20” 20 ____ 400.  The H.P. is 40.

The following rules will be found more professionally accurate from an engineering standpoint, though the term “horse-power” is not now generally employed.

To find the Nominal Horse-power.—­For non-condensing engines:  Multiply the square of the diameter of the cylinder in inches by 7 and divide the product by 80.  For condensing engines:  Multiply the square of the diameter of the cylinder in inches by 7 and divide the product by 200.

To find the Actual Horse-power of an engine, multiply the area of the cylinder in square inches by the average effective pressure in pounds per square inch, less 3 lb. per square inch as the frictional allowance, and also by the speed of the piston in feet per minute, dividing the product by 33,000, and the quotient will be the actual horse-power.

“SCALING” COPPER PLATES

To “scale” copper plates they may be put over a charcoal or coke fire to slowly sublimate the quicksilver.  Where possible, the fireplace of a spare boiler can be utilised, using a thin red fire.  After the entire evaporation of the quicksilver the plates should be slowly cooled, rubbed with hydrochloric acid, and put in a damp place overnight, then rubbed with a solution of sal ammoniac and nitre in equal parts, and again heated slowly over a red fire.  They must not be allowed to get red hot; the proper degree of heat is indicated by the gold scale rising in blisters, when the plates should be taken from the fire and the gold scraped off.  Any part of the plate on which the gold has not blistered should be again rubbed with the solution and fired.  The gold scale should be collected in a glass or earthen dish and covered with nitric acid, till all the copper is dissolved, when the gold can be smelted in the usual way; but after it is melted corrosive sublimate should be put in the crucible till a blue flame ceases to be given off.

A Second Method

The simplest plan I know is to have a hole dug nine inches deep by about the size of the plate to be scaled; place a brick at each corner, and on each side, halfway between, get up a good fire; let it burn down to strong embers, or use charcoal, then place the plate on three bars of iron extending between the three pairs of bricks, have a strong solution of borax ready in which soak strips of old “table blanket,” laying these over the plate and sprinkling them with the borax solution when the plate gets too hot.  After a time the deposit of mercury and gold on the plate will assume a white, efflorescent appearance, and may then be readily parted from the copper.

Another Method