Page 171 - James Rodger Fleming - Fixing the sky

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came across . . . lead iodide, antimony, and silver iodide.” Powdered lead iodide
produced “a reasonable number of crystals” in Schaefer’s cold box, a phenom-
enon that Schaefer attributed to the hexagonal shape of the molecules, but still
they could not get a good result: “Well, I couldn’t figure this out; so I was just
puttering around and I decided to see just what happened when I put metal
smoke in there [from silver]. I was amazed—the ice box was just swimming with
ice crystals—colossal numbers. . . . Then I remembered silver iodide and made
smoke. . . . Vaporizing silver iodide worked like a charm.” Vonnegut’s laboratory
notebook indicates that he had identified lead iodide as an artificial nucleating
agent by November 6, 1946. After numerous trials, he finally got iodine vapor
and metallic silver to work on November 14: “Hallelujah! the nucleation was
even more wonderful.” By November 18, just four days after Schaefer’s outdoor
experiment, Vonnegut had found out that it was the silver iodide that did the job.
Because of its hexagonal structure, silver iodide imitates ice condensation nuclei,
causing “explosive ice growth” in supercooled clouds. 55
Vonnegut soon started seeding experiments with ground-based silver iodide
generators, but found it hard to tell where the smoke was going and what effect
it was having. He did some inconclusive aircraft tests in December 1947, but “felt”
that the experiments he conducted with GE meteorologist Ray Falconer with a sil-
ver iodide generator on the summit of Mount Washington were the most satisfy-
ing: “I feel darn sure we got some nice results . . . we caused quite a nice snow squall
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downwind from the generator on air as it goes up over the mountain.” He had yet
to develop reliable techniques for following the particles and measuring their con-
centrations. The General Electric News Bureau, however, was quick to claim credit:

If generators can be used on the ground to introduce silver iodide or other foreign
particle nuclei into huge masses of air, it might be possible to alter the nature of
the general cloud formation over the northern part of the United States during
winter. . . . It would prevent all ice storms, all storms of freezing rain, and icing con-
ditions in clouds. The amount of heat absorbed by sunlight would be changed. It
should be possible to change the average temperature of some regions during win-
ter months. 57

Vonnegut, who was less sanguine, pointed out that silver iodide has its own
problems. It is persistent in the environment and can activate long after its release
in clouds of proper temperature; dry ice, though, works immediately and then
sublimates. He recalled in an interview, “This is bad, I think, for commercial
cloud-seeding operations, because I think they’re playing with fire releasing this
stuff all over the place and I think it’s a shame they haven’t shown any sense of

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