Inorganic in nature, this compound is the acidic anhydride derived from chromic acid, and is often marked under that name when labelling. Dark purple under anhydrous conditions, chromium trioxide turns a bright orange when added to aqueous solutions, and is soluble in water concomitant with hydrolysis. The primary industrial use of chromium trioxide is used in various metal industries for chrome electroplating. Due to its potent nature as an oxidiser, chromium trioxide is also classified as a potential carcinogen according to numerous industrial exposure studies. To produce chromium trioxide, quantities of sodium chromate (chrome salt) or sodium dichromate are treated with sulfuric acid. Mass quantities of this substance are produced each year using this method, often as much as 100 million kilograms or more. Given the popularity of chrome plating as an extremely effective rust resistant means of preserving steel, chromium trioxide is used in everything from high end aluminum alloy performance car wheels to rifled barrels on high end firearms.