Safe Internal Pressure

—The safe internal pre ure on cylindrical shells is found according to the following rule, which has been adopted by the United States Board of Supervising Inspectors, and any boiler shell can be determined by this rule: Multiply one sixth of the lowest tensile strength found stamped on any plate in the cylindrical shell by the thickne expre ed in inches or parts of an inch of the thinnest plate in the same cylindrical shell, and divide by the radius of half diameter, also expre ed in inches, and the result will be the pre ure allowable per square inch of surface for single riveting, to which add twenty per cent for double riveting.