Sidney Thomas, in the 1870s, solved the problem of how to remove phosphorus from steel in the Bessemer process. Before then, the Bessemer converter, unlike the earlier puddling method, was inefficient at removing phosphorus, so that only ores in this element could be employed. Thomas recognized that the secret was to remove it in a basic slag by using lime or magnesia in the converter lining. George Snelus also made contributions to these problems along the same lines, and the principle of ladle and furnace treatments to improve the purity and properties of the steel continues in developments to this day.