To find the fire-grate surface of flue boilers.

Square the nominal horse-power, and divide it by the heating surface in square yards; the quotient will be the fire-grate surface in square feet—

or, one square foot of fire-grate surface per nominal horse-power.

To find the healing surface of a flue boiler.

Square the nominal horse-power as indicated by the manufacturer's receipt or bill of sale, and divide that by the fire-grate surface in square feet; the quotient will be the heating surface in square yards.

Capacity of boiler flue.

One cubic yard of boiler capacity for each nominal horse-power. Steam-room should be about eight times the contents of the cylinder of the engine supplied with steam by the boiler.

Tubular or marine boilers.

Each nominal horse power requires the evaporation of one cubic foot of water per hour; 12 square feet of heating surface, only three-fourths of the whole tube surface being taken as effective; and 30 square inches of fire-grate per nominal horse-power. The sectional area of the tubes to be about one-sixth of the fire grate.

General rule for all classes of boilers.

• Twelve square feet of heating surface and three-fourths square foot of fire-grate per nominal horsepower, are very good proportions.

Temperature Indicated By The Color Of The Fire.

To determine the temperature of a furnace fire from the color of the flame :

Faint red...........9600 F.

Bright red...........1,300° F.

Cherry red..........1,6oo° F.

Dull orange..........2,000° F.

Bright orange.........2,100° F.

White heat..........2,400° F.

Brilliant white heat......2,700° F.