AbstractExperimental studies of the mixing of coaxial streams of a natural gas and air at atmospheric pressure were made at Reynolds numbers of 44,000 and 79,000 under conditions where the turbulent‐velocity profile of nearly uniform flow was altered as little as feasible by the blending of the two streams.Total diffusivities of natural gas in air for the region near the center of the conduit were computed from the data for turbulent, steady, nonuniform flow. The total diffusivities were found to be rather complicated functions of the conditions of flow. Limitations in the configuration of the apparatus did not permit a study of the behavior of the total diffusivities to be made over as wide a range of flow rates as would be necessary to investigate the large‐scale trends indicated by this st