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,
Interstitial element Interstitial element An interstitial element is an impurity found in "pure" metals or crystals. The quantity of these elements affect the physical properties of the host material. They can be introduced during the manufacturing process. The most common interstitial elements in metals are hydrogen, carbon, nitrogen, and oxygen. These elements are small enough to fit between normal crystalline lattice locations. In contrast, those elements that replace locations in the crystalline structure are called substitutional elements. An example of the effects of interstitial elements on metal properties can be found in grade 1–4 titanium. Although the grades 1–4 are considered commercially