We perform quantitative investigations of double-diffusive convection in a setup that is extremely easy to implement and to observe. In this setup, a drop (containing a surfactant, as destabilizing substance, and glycerine, as stabilizing substance, stirred in water) is injected at the bottom of a dish filled with water. After a few minutes, surfactant cells are formed. Later, fingers transporting surfactant grow upwards at the vertices of these cells. The size of the cells and their growth time T-em are observed with a light microscopes also, these quantities are estimated analytically and determined from PDE simulations. We obtain power laws for the dependence of A and T-em on the initial concentration of the stabilizing substance; the exponents in these laws are widely independent of the experimental conditions and on the model assumptions. (C) 2002 Elsevier Science Ltd. All rights reserved.