Mass transfer rates have been measured at 30°C. over a Reynolds number range of 1 to 130 for the solution of 3/8-in. diameter spheres of benzoic acid for both upflow and downflow streams. These are compared with similar results for 3/4-in. diameter spheres and show a gradual transition from forced to free convection. The interaction between the two effects is complex but less marked for the smaller spheres. Free convective effects do not disappear entirely until a Reynolds number of about 250 for the 3/8-in. spheres, compared with a value of 750 given for 3/4-in. spheres in the previous work (6).