A AC and PA are two kind of organic compounds. Acetyl Acetone Copper and Phthalic Anhydride. They were chosen among over thirty kinds of organic compounds based on the experiments on their performance in ice nucleation via a cold chamber at Beijing University. They are approved by the expert concerned in Wuhan, in April of 1984.A comprehensive decriplion is given here on AAC and PA, including their performance in ice nucleation,physical and chemical property,poiso-onusness,price.the materials from which they are made and the method the by which the particles are generated as well as several experiments in the field.