Conversion. Beverage containers to aviation oxygen cylinders. Before completion of the fourth and final welding operation in the manufacture of shatterproof oxygen cylinders for high altitude flying, all straps are subjected to physical tests to determine the strength of the weld. Occasional radiographic inspections are made to insure the quality of workmanship and materials after the atomic welding machine has brought the two halves of the cylinder together and made into one unit. The operator, looking through a specially designed dark safety glass, rotates the shell by sight to insure a perfect and uniform union of the two halves. Firestone, Akron, Ohio. Sourced from the Library of Congress.