Cappelen Smith was employed in the metallurgical industry working from 1895–96 for Chicago Copper Refining Company, during 1896–1900 for the Anaconda Copper Mining Company and from 1901–10 as head metallurgist for Baltimore Copper Smelting and Rolling Company in Perth Amboy, New Jersey. It was while at this company, that he and William H. Peirce developed the, which revolutionized the Manhès-David process.
Peirce-Smith converter
The Peirce-Smith converter, introduced in 1908, improved significantly the copper converting process. Before this improvement, the converter was a long cylindrical vessel, lined with sand and clay. It was developed by two French engineers, Pierre Manhès and from 1880 to 1884. Their copper-converting process, named the Manhès-David process, was directly derived from the Bessemer process. In this horizontal chemical reactor, where air was injected into copper matte, a molten sulfide material containing iron, sulphur and copper, to become molten blister, an alloy containing 99% copper. But the basic slag produced during the blowing combined with the acid silica refractory lining, thereby causing a very short lifetime of the lining. By developing a basic refractory material adapted to the matte refining process, Cappelen Smith and William H. Peirce found a way to drastically increase the lifetime of the lining. It has been stated that, in some cases, the process allowing an increase from 10 to 2500 tons of copper produced without relining the converters. A reduction of the cost of copper converting from 15–20 USD to 4–5 USD has been stated. The Peirce-Smith converter replaced quickly the Manhès-David Converter : by March 1912, the Peirce-Smith Converting Co claimed that "over 80% of the copper produced in is being converted either in P-S type converters or on basic lining, under license, in the old acid shells". It is still in use today, although the process has been significantly improved since then. In 2010, with 250 converters working in the world, the Peirce-Smith converters refine 90% of the copper matte.
In 1920 Cappelen Smith was honored with the gold medal of the Mining and Metallurgical Society of America for distinguished service in the art of hydrometallurgy. In 1925, he was made a commander 1st Class in the Royal Norwegian Order of St. Olav. He was made a member of the Royal Norwegian Scientific Society during 1926. He was also commander of the Chilean Al Merito-order and was awarded an honorary doctorate at Drexel Institute of Technology. In 1930, Cappelen Smith helped finance the installation of the Steinmeyer organ in the Nidaros Cathedral for the 900th anniversary of the Battle of Stiklestad.