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Homogeneous nucleation rate measurements have been made on ethanol, n-propanol, and i-propanol vapors over a range of temperatures and supersaturations. The Becker–Doring–Zeldovitch nucleation rate expression has been scaled so as to give good agreement with the measured nucleation rates. The same scaling factors are also used to compare calculated critical supersaturations with experimental data obtained from this investigation and a variety of other sources. The agreement is good in all cases. The nucleation rate measurements and the critical supersaturation data from this investigation reveal anomalous behavior for ethanol near 260 K and for n-propanol near 275 K.

The temperature variation of the critical supersaturation for water vapor has been measured using a diffusion cloud chamber. By attaching a layer of glass wool to the upper plate of the chamber, the persistent refusal (in previous experiments) of water to wet this plate has been overcome. As a result, for the first time measurements without appreciable scatter have been achieved for water vapor. The resulting temperature dependence agrees reasonably well with that predicted by the classical Becker-Doering-Zeldovitch theory, while the experimental curve is shifted by approximately 8% from the classical prediction.

We report new results of nucleation measurements carried out in our laboratory at a variety of constant total pressures for 1-propanol vapor with nitrogen, helium, and hydrogen as background gases and for 1-butanol vapor with nitrogen and hydrogen as background gases. In addition, we report new results of nucleation experiments carried out at a variety of constant temperatures for 1-butanol with helium and hydrogen as background gases. The 1-butanol constant temperature results compare favorably with the results of the 1-butanol constant total pressure experiments, and the constant total pressure data for 1-propanol obtained in this investigaton compare favorably with constant temperature results obtained from 1-propanol experiments described in the literature. The results of this investigation (continue to) suggest a significant role of the background gas in the nucleation process. Our constant pressure and constant temperature experiments reported here give new results that reinforce our earlier observations that as the amount of background gas is increased, the rate of nucleation decreases. We continue to find that the magnitude of this effect becomes greater as the molecular weight of the condensable increases. Similarly, for all of the alcohols we have investigated, this effect becomes greater as the formula weight of the background gas increases, and the slope of the dependence of the critical supersaturation on total pressure increases as the temperature decreases.