Simple heterogeneous equilibria can be elucidated by determining the total amount of solid that goes in the gas phase under the action of a known amount of gaseous solvent at a given temperature. This method was first tested satisfactorily with the germanium-iodine system, for which thermodynamic data are already available, and then applied to the germanium-bromine system. The data make it possible to calculate the ratio between total density of germanium atoms and total density of halogen atoms in the gas phase within a wide range of temperatures and pressures. These calculations enable one to predict the direction and the amount of diffusive vapor transport in closed or open vaporgrowth systems. © 1964, The Electrochemical Society, Inc. All rights resereved.