The invention has as subject matter a rotary tube, especially for a rotary tube kiln for the production of carbon, with several mixing elements arranged in the inner space of the rotary tube for a thorough mixing of a charged material. The rotary tube comprises a transitional area from a smaller inside cross section to a larger inside cross section of the rotary tube. The mixing elements are formed in the transitional area and/or are arranged in such a manner that the charged material is transported during operation by the mixing elements toward the smaller inside cross section. The result is an excellent thorough axial mixing and blending of the charged material, which results in an increased homogeneity of the activated carbon produced.