BOILERS FOR STATIONARY ENGINES.

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cubical contents of the shell, with or without inside flues. Sup-posing, for the sake of illustration, a Cornish boiler of 40 nominalhorse-power was required, multiply the horse-power by 27 cubicfeet, and the result will be the cubical contents, thus—

40 X 27 = 1080 cubic feet.

Length and Diameter .—The length of the boiler should be aboutthree and one-half times the diameter for moderate power, or up toabout 20 horse-power inclusive; above that size five times thediameter can be adopted—a little more or less can do no harm. Tofind the diameter, multiply 1080, the cubical contents required, bythe constant i'28, dividing the result by the proportion of the dia-meter to the length, say five times, and the cube root of the quotientwill be the diameter, which, multiplied by 5, gives the length of theboiler nearly.

-g- =n/ 276-48 = say 6-5x5 = 32-5.

The length of the boiler, in round numbers, is 32-5 feet, and6'5 feet in diameter. To check the calculation, the area of 6-5 feetin diameter is 33-18 square feet X 32-5 = 1078-35 cubic feet, withina trifle of what is required.

Heating Surface, Fire-grate , and Flue Area .—The heating surfaceshould not be less than 1 square yard, or 9 square feet, per nominalhorse-power; but in ordinary boilers it will be found that more thanthis can be conveniently got. The area of the fire-grate, when the fur-nace is underneath the boiler, should be 1 square foot, and when thefurnace is in a flue, forming part of the boiler, -75 of a square foot willbe sufficient, per nominal horse-power. The length of the fire-grateshould never exceed 7 feet. When the furnaces are placed inside ofthe boiler, for small diameters, the inside flues should be 2 feet 6 inchesin diameter, and certainly not less than 2 feet 3 inches. When smallerthan this, the fires do not burn well, and they are troublesome tofire; for large diameters of boilers, the furnace flues can be 3 feet

3 inches in diameter. The area of the furnace flues should beabout 28 square inches per nominal horse-power, a little more doingno harm; thus for 40 horse-power, we have for two furnaces—

40 X 28 = 1120 -r- 2 = 560 square inches,

equal say 2 feet 3 inches diameter for each flue in the boiler, and

4 feet 6 inches as the sum of the width for both; thus, for the