The largest antimony smelter in the world in 1945 was just north of Laredo in Webb County. Initially it had been at San Luis Potosí, Mexico, operated by a British firm owned by the Cookson family and founded in 1704. The duty placed on foreign antimony in the 1920s had encouraged domestic production to free the United States from dependence on Chinese antimony supplies. At that time, the smelter company moved north along the railroads to remain as near as possible to the source of Mexican ore, which was produced chiefly at San Luis Potosí and Oaxaca, and reestablished the smelter at Laredo. Known for a time as Lead Industries, this firm by 1930 had become the Texas Mining and Smelting Company. H. P. Henderson, the first president of this company, was succeeded by V. L. Kegler in 1939. At its Laredo location the smelter burned natural gas and Alabama coke. During World War II, when the British government exchanged its assets in America for weapons and supplies, Texas Mining and Smelting became an American firm known as National Lead, which operated the smelter until it ceased production in 1976. In 1977 the original British firm, then known as the Cookson Group, once again acquired the Laredo operation. At that time Cookson (under the name Anzon, Limited) produced antimony and zircon in Europe. The Laredo operation became Anzon American and later Anzon, Incorporated. Among the company's products is an antimony oxide known as TMS (from Texas Mining and Smelting Company).