A cold arc discharge is used to decompose natural gas or methane into its gaseous constituents and carbon in the form of solid particles. The gaseous constituents obtained are mainly hydrogen and acetylene and they are produced in admixture with unreacted natural gas or methane. The cold arc discharge is generated by a pulsating high voltage discharge imparted through a capacitor to a high voltage electrode or a plurality of high voltage electrodes or through a high voltage electrode to a plurality of capacitor-connected electrodes placed in a reaction zone. The apparatus for performing this process may have a tubular reactor with a cylindrical ground electrode in the middle and a cylindrical outer wall through which the high voltage electrode or electrodes extend into the reaction zone. The apparatus may also have a cylindrical shaft in the middle made of dielectric material in which a plurality of electrodes are embedded, this shaft being surrounded by a high voltage tubular electrode. Natural gas or methane is passed through the reaction zone where it is subjected to the cold arc discharge or discharges and the resulting products flow out of the reactor and solid carbon particles are separated from the remaining gases that are then analysed.