In conjunction with his work for Napier and Sons, Kirkaldy undertook a long series of tensile load tests between 1858 and 1861.

The testing machine is 47 feet 7 inches long, weighs some 116 tons, and was designed to work horizontally, the load applied by a hydraulic cylinder and ram.

He set up business in Southwark in 1866, performing tests for external clients on materials used in engineered structures such as bridges.

He developed ways of examining the microstructures of materials using a simple optical microscope after polishing and etching specimens taken from components.

Since he tested several samples of each of the lower and upper lugs, he was able to show that they exhibited a range of strengths, the lowest results being caused by defects like blow holes in the cast metal.

Some were reused in local houses, and when they were demolished in the 1960s, some were removed to the Royal Museum of Scotland in Edinburgh, where they are on public display.