An experimental study of mired-convection heat transfer flow of a CuSO4 + H2SO4 + H2O solution in a horizontal channel was performed. Unstable temperature gradients imposed by a heated bottom initiated an ascending (secondary) flow of light boundary layer fluid into the free stream. The shadowgraph technique was used to visualize the flow and to determine the nature and effect of thermally driven secondary flows in a horizontal channel with heated top and bottom surfaces and insulated side wads. The ranges of the parameters studied in the present work for the square channel are Pr = 5-7, Re = 100-1,000, and Gr(qb) = 2.8 x 10(6)-2.5 x 10(7). Flow visualization revealed the existence of four regimes corresponding to laminar forced convection, laminar mired convection, transitional mixed convection, and turbulent free convection. Also, the onset of secondary flow was found to be delayed by decreasing the Grashof number and/or by increasing the Reynolds number. A direction for future study of mixed thermosolutal convection is also pointed out.