MISCELLANEOUS TECHNICAL DATA To find diameter of a circle multiply circumference by .31831. To find circumference of a circle multiply diameter by 3.1416. To find area of a circle multiply square of diameter by .7854. To find surface of a ball multiply square of diameter by 3.1416. To find side of an equal square multiply diameter by .8862. To find cubic inches in a ball multiply cube of diameter by .5236. Doubling the diameter of a pipe increases its capacity four times. Double riveting is from 16 to 20 per cent stronger than single. One cubic foot of anthracite coal weighs about 53 pounds. One cubic foot of bituminous coal weighs from 47 to 50 pounds. One ton of coal is equivalent to two cords of wood for steam purposes. A gallon of water (U.S. Standard) weighs 8-1/3 lbs. and contains 231 cubic inches. There are nine square feet of heating surface to each square foot of grate surface. A cubic foot of water contains 7 1/2 gallons, 1728 cubic inches, and weighs 62 1/2 lbs. Each nominal horse power of a boiler requires 30 to 35 lbs. of water per hour. To sharpen dull files lay them in dilute sulphuric acid until they are eaten deep enough. A horse power is equivalent to raising 33,000 lbs. one foot per minute, or 550 lbs. one foot per second. To find the pressure in pounds per square inch of column of water, multiply the height of the column in feet by .434. Steam rising from water at its boiling point (212 degrees) has a pressure equal to the atmosphere (14.7 lbs. to the square inch).