Experimental Studies of Organic Ice Nuclei

Abstract

The ability of 329 selected organic compounds to nucleate ice has been tested by three methods. Their activity was found to depend strongly on the method of preparation. More than 20 compounds were found to nucleate ice at temperatures above ?5C when freshly ground. Some meta and para derivatives of benzene showed excellent activity. Particles prepared by condensation were less active, the only newly-discovered material effective above ?5C being 1,5-dihydroxynaphthalene. Its use as a cloud seeding agent is suggested. Crystals of effective materials generally have molecules which display rotational symmetry. The role of molecular symmetry is discussed in connection with the formation of crystal planes with dense hydrogen bonding groups. The behavior of organic nuclei with nonsymmetrical molecules is also considered.