Acetylene, uh SEHT uh leen, is a colorless, flammable gas used for welding and for preparing other chemical compounds. Its chemical formula is C2H2. Acetylene is poisonous if inhaled. It also forms explosive mixtures with air. Edmund Davy, an English chemist, first produced acetylene in 1836. The gas was forgotten until 1860, when the French chemist Marcellin Berthelot discovered a way to synthesize the gas from carbon and hydrogen, using an electric arc.