We present data from the first systematic studies of binary condensation in supersonic nozzles. The apparatus used to conduct the experiments is described in detail, and the important issues of stability and reproducibility of the experiments are discussed. Experiments were conducted with water, ethanol, propanol, and binary mixtures of these compounds. Onset was determined in the temperature range of 190-215 K, and for each mixture composition the pressures of the condensible species at an onset temperature of 207 K were determined. For the ideal ethanol-propanol mixtures, the onset pressures at constant temperature vary almost linearly between those of the pure components. In contrast the isothermal onset pressures for the nonideal water-ethanol and water-propanol mixtures lie below the straight line joining the pure component values. This large reduction in the total pressure of condensible at onset for the aqueous alcohol mixtures is indicative of a strong mutual enhancement in the particle formation process.