An experimental study of mixed-convection mass transfer flow of a CuSO4 + H2SO4 + H2O solution in a horizontal channel is performed using an electrochemical system. Unstable concentration gradients imposed by a cathodic bottom initiate an ascending (secondary) flow of light boundary-layer fluid into the free stream. To visualize the flow, the shadowgraph technique is used. Electrical measurements are used to obtain mass transfer rates and to infer a Sherwood number. The ranges of the parameters studied in the present work for the square channel are Sc = 1,700-2,300 Re = 100-1,000, and Ra = 7.09 x 10(8)-2.60 X 10(9).