Rhodium is a rare, silver-white, metallic element that serves mainly as a catalyst, a substance which increases the speed of a chemical reaction. Rhodium is a catalyst in the production of nitric acid and various organic compounds and medicinal drugs. It is also used in catalytic converters, which reduce pollutants in automobile exhausts. Rhodium alloys (metal mixtures) are used in aircraft turbine engines, electric connections, and reflective surfaces of mirrors and searchlights.