. Carnegie Institution of Washington publication. n6 VAPOR NUCLEI AND Fig. 54.—Supersaturations (S) of media air-water and alcohol-water, and estimated radius (r cm.) of smallest efficient nuclei, at different exhaus- tions (dp), m, molecular radius. Table 45. Since pT is the adiabatically reduced vapor pressure (with- out condensation) in the vol- ume expansion due to the drop of pressure (dp) and pM the normal vapor pressure at the same temperature (d = 2 7 30 -f- /2 in table 1), r follows from the equation. The values of pTlpm and r so found are both given in table 45, and have been
. Carnegie Institution of Washington publication. n6 VAPOR NUCLEI AND Fig. 54.—Supersaturations (S) of media air-water and alcohol-water, and estimated radius (r cm.) of smallest efficient nuclei, at different exhaus- tions (dp), m, molecular radius. Table 45. Since pT is the adiabatically reduced vapor pressure (with- out condensation) in the vol- ume expansion due to the drop of pressure (dp) and pM the normal vapor pressure at the same temperature (d = 2 7 30 -f- /2 in table 1), r follows from the equation. The values of pTlpm and r so found are both given in table 45, and have been constructed in the chart (fig. 54), where their relation to the usual order of molecular size is also indi- cated. Clearly these values of r, the radius of the nuclei differing so little from molec- ular radii (say io~8), can only indicate an order of values; for apart from the difficulties above enumerated in com- puting d, r depends on sur- face tension (T), which has no meaning for molecular dimen- sions. Granting this, it is none the less remarkable that the values of r obtained should be so nearly alike for water and alcohol where different constants (T, R, s, etc.) occur throughout; in other words, that at a given temperature a given drop of pressure will condense both vapors on nuclei of about the same size. In so far as these estimates are admissible it follows that the alcohol- air nucleus is larger than the water-air nucleus, since in the former case coronal condensation begins at about dp = 15 cm. where r — io~7 cm. and in water vapor it begins at dp = 26 cm. where r= 4 X io~8 cm. about, less than half as large. These relations once established are retained through all successions of nuclei, as the following data for alcohol vapor in comparison with water vapor show. It is a little difficult to under- stand why the ionized nuclei in alcohol vapor should, like the colloidal nuclei, be larger than the corresponding cases for water vapor, unless the ions are aggrega
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