Divide the square of the thickness of the plate in inches by the square of the radius of the shell in inches, and multiply the quotient by 5625 for a head of copper; by 9000 tor a head of wrought-iron; and by 15.000 for a head of steel.

Suppose the heads of a boiler are of steel, \ inch in thickness, and that the diameter of the boiler is 24 inches: .25 (the square of1/2), divided by 144 (the square of the radius), is .00174, and the product of .00174 and 15, 000, 26 1bs., is the pressure required. B.

Boilers, Seating surface of -Note: In the following rules all dimensions are to be taken in feet.

(a) Cylindrical boilers. Take the product of (1) the diameter of the boiler, (2) the length of the boiler, and (3) 1.5708.

Suppose a given boiler has a diameter of 36 inches, and a length of 20 feet, its heating surface is the product of 3, 20, and 1.5708, or about 94-1/4 square feet