Welding gas is a type of fuel used in welding and cutting processes. Two common types of welding gas are ACETYLENE and ethylene. ACETYLENE is a hydrocarbon gas composed of two carbon atoms and four hydrogen atoms, and it is the hottest burning fuel gas. Ethylene is an unsaturated hydrocarbon gas composed of two carbon atoms and four hydrogen atoms, and it is the most commonly used fuel gas. Both gases are used in welding and cutting processes to create strong bonds between metals.