The Nucleation of Supercooled Water by Various Chemicals

A cooled expansion chamber was used to form water clouds upon aerosol particles of a variety of chemical substances of low solubility. The proportion of ice crystals to water drops in the clouds was observed at a series of decreasing temperatures. In this way the ice-forming ability of the various chemicals could be assessed. In general it was found that for the particular substances chosen, the chemicals which caused water to freeze at the highest temperatures were those in which the lattice spacing approached most closely that in the ice lattice. Some exceptions to this rule show that geometrical considerations alone are insufficient to account for nucleating ability.