Our first Scottish historic bridge to visit was the Forth Railway Bridge in Queensferry, and, thanks to British Airways flight from Edinburgh to London’s Heathrow airport at the end of our trip, it was our last bridge to view. It was a spectacular sight from the air, this 1890 bridge spanning the wide and deep Forth Estuary, a fitting end to Nan’s three-week self-guided tour of some of Scotland’s famous historic bridges.
Construction of the Forth Railway Bridge was under the direction of Sir William Arrol, and it was his invention of a hydraulic riveter that increased the riveting output on the Forth Railway Bridge. I was not familiar with the Scottish engineer Sir William Arrol but through books and other publications purchased while in Scotland I discovered him to be a skilled innovator in the riveting process. “Bridges” by Sir William Arrol & Co. Ltd., Dalmarnock Iron Works, Bridgeton, Glasgow, 1909, is a rare used book we purchased at Caledonia Books in Glasgow, a forty year documentation of bridge construction and specifications of Sir William Arrol & Company.
One section from this book caught my attention under “General Specification for Workshop Buildings.” In the section on Cast Iron, Arrol writes: All castings shall be of the best tough grey metal of such a strength that a bar 1 in. thick by 2 in. deep placed upon bearings 3 ft. apart will sustain without fracture a weight of 27 cwt. placed at the centre with a deflection of not less than 1/3 in.” Cast iron is often confused with wrought iron, another metal less known and no longer produced; Arrol fabricated bridges with both wrought and cast iron, and many of Arrol’s nineteenth century cast iron bridges are still in vehicular use in the twenty-first century.
For those interested in learning more about cast iron, Knight Foundry in Sutter Creek, California, USA, offers hands-on training for craftsmen, engineers, museum and history professionals, and the general public in the art of sand casting of cast iron. Knight Foundry is the best professionally preserved 19th-century industrial complex for the continued study of a historic industrial process still used today in metal fabrication.
