HYDROCARBON, in chemistry, a compound of carbon and hydrogen. The simplest hydrocarbons are gaseous, many are liq uid, and the more complicated are solid. Many occur in nature: for example, natural gas, petroleum and paraffin are mainly com posed of such compounds; other natural sources are india-rubber, turpentine and certain essential oils. They are also revealed by the spectroscope in stars, comets and the sun. Of artificial produc tions the most fruitful and important is provided by the destruc tive or dry distillation of many organic substances; familiar ex amples are the distillation of coal, which yields ordinary lighting gas, composed of gaseous hydrocarbons, and also coal tar (q.v.) which, on subsequent fractional distillation or treatment with solvents yields many liquid and solid hydrocarbons, some of high industrial value. For details reference should be made to the articles wherein the above subjects are treated. From the chemical point of view the hydrocarbons are of fundamental importance, and, on account of their great number and still greater number of derivatives, they are studied as a separate branch of the science, namely, organic chemistry. (See CHEMISTRY : Organic.)