<PICT:0621031/III/1> Carbon black is produced by introducing reactant hydrocarbons into one end of an elongated unobstructed cylindrical reaction chamber 10, introducing hot combustion gases, or a free oxygen-containing gas, or a mixture of the latter with gaseous fuel tangentially to the inner surface of the furnace wall through one or more inlets 15, regulating the amount and temperature of the gas so introduced to provide temperatures sufficient to decompose a portion of the reactant hydrocarbon to carbon black, and cooling the products of decomposition, e.g. by a water spray 14. The furnace is comprised by a refractory sillimanite or alundum liner 11, insulation 12 and a steel shell 13. The velocity of the gas p admitted through inlets 15, which may be spaced along the length of the chamber, is high so as to maintain a layer of flame following a helical path on the inside of the chamber wall. Air, oxygen, or a mixture thereof, may be admitted to inlet tube 16 with natural gas, and both may be preheated to 1000-2800 DEG F. or more. Gas from gasoline extraction plant, refineries residue gas, butane, and vaporized oils and distillates may also be used as the reactant hydrocarbons. The air or gas, or both, fed to the tangential burners may be preheated. The temperature within the chamber may be 2000 DEG to 3300 DEG F. The Specification as open to inspection under Sect. 91 comprises also a reaction chamber having a constriction therein and in which an annular space is provided around the mixing inlet tube 16. This subject-matter does not appear in the Specification as accepted.ALSO:For the comparison of the properties of furnace and channel black with a carbon black made by decomposing a hydrocarbon in a chamber on the inside wall of which is maintained a circulating flame, (see Group III), batches of rubber compound are prepared containing smoke sheet, carbon black, zinc oxide, sulphur, stearic p acid, phenyl b naphthylamine, "Captax" (Registered Trade Mark) and pine tar.