Heavy metals is improved with the addition of thorium. Tellurium is added to copper and steel alloys to improve their machinability; and to lead to make it harder and more acid-resistant. The biocidal effects of some heavy metals have been known since antiquity. Platinum, osmium, copper, ruthenium, and other heavy metals, including arsenic, are used in anti-cancer treatments, or have shown potential. Antimony (anti-protozoal), bismuth (anti-ulcer), gold (anti-arthritic), and iron (anti-malarial) are also important in medicine. Copper, zinc, silver, gold, or mercury are used in antiseptic formulations; small amounts of some heavy metals are used to control algal growth in, for example,
Refractory metals and in many other ways. Tungsten can be found in printing inks, x-ray screens, photographic chemicals, in the processing of petroleum products, and flame proofing of textiles. Niobium is nearly always found together with tantalum, and was named after Niobe, the daughter of the mythical Greek king Tantalus for whom tantalum was named. Niobium has many uses, some of which it shares with other refractory metals. It is unique in that it can be worked through annealing to achieve a wide range of strength and elasticity, and is the least dense of the refractory metals. It can also be found