Arsenical copper contains up to 0.5% arsenic which, at elevated temperatures, imparts higher tensile strength and a reduced tendency to scaling. It is typically specified in boiler work, especially locomotive fireboxes.^[1][2][3] It also helps prevent embrittlement of oxygen-free copper by bismuth, antimony and lead by the formation of complex oxides. Copper with a larger percentage of arsenic is called arsenical bronze, which can be work-hardened much harder than copper.