On July 4, 1874, a bridge, designed by J. B. Eads, was dedicated which spans the Mississippi River at St. Louis. It was the first time steel had been used in such a structure. Crucible steel, eventually chromium steel, was specified for support arches and anchor bolts. Special testing machines were built to insure the required tensile strength of 100,000 lb/in² for each bolt. Bolts were 6 inches in diameter and up to 36 feet long. The support arches were made of tubes, each tube consisting of six carefully matched staves, like those in a barrel. The modulus of elasticity for the tubes was 26 to 30 million lb/in². Recent tests on a sample from the bridge show the composition is 0.53 carbon, 0. 2 manganese, 0.4 chromium, 0.12 silicon, 0.02 sulphur, balance iron with a ferrite-pearlite microstructure. Hardness is 1.95 to 250 HB. -- AATA