Preparation of Colloidal Silver-Iodide Water-Suspensions for Nucleation of Supercooled Clouds

IN the course of a search for a suitable form in which particles of silver iodide can serve as nucleating agents of a supercooled cloud, Vonnegut tested 1 an aqueous solution of silver iodide (200 gm. of silver iodide and 100 gm. of ammonium iodide in a mixture of 750 c.c. of acetone and 250 c.c. of water). It is reported by him that “solutions can be diluted any desired amount with acetone; dilution with water causes precipitation of AgI”. On the other hand, it was known 2 that in experiments on artificially induced rain from supercooled clouds in Algeria, a colloidal aqueous suspension (1 1,000, 1/10,000 by weight) of silver iodide was used with success. Since no particulars of this colloidal aqueous suspension were available, it was decided to try to produce a colloidal suspension ( a ) as stable as possible, ( b ) one that can be diluted to any proportion with water.