Ice-nine is a fictional material appearing in Kurt Vonnegut's novel Cat's Cradle. Ice-nine is supposedly a polymorph of water more stable than common ice (Ice Ih); instead of melting at 0 °C (32 °F), it melts at 45.8 °C (114.4 °F). When ice-nine comes into contact with liquid water below 45.8 °C (thus effectively becoming supercooled), it acts as a seed crystal and causes the solidification of the entire body of water, which quickly crystallizes as more ice-nine. As people are mostly water, ice-nine kills nearly instantly when ingested or brought into contact with soft tissues exposed to the bloodstream, such as the eyes.
In the story, it is developed by the Manhattan Project in order for the Marines to no longer need to deal with mud, but abandoned when it becomes clear that any quantity of it would have the power to destroy all life on earth. A global catastrophe involving freezing the world's oceans with ice-nine is used as a plot device in Vonnegut's novel.
Vonnegut came across the idea while working at General Electric:
- The author Vonnegut credits the invention of ice-nine to Irving Langmuir, who pioneered the study of thin films and interfaces. While working in the public relations office at General Electric, Vonnegut came across a story of how Langmuir, who won the 1932 Nobel Prize for his work at General Electric, was charged with the responsibility of entertaining the author H. G. Wells, who was visiting the company in the early 1930s. Langmuir is said to have come up with an idea about a form of solid water that was stable at room temperature in the hopes that Wells might be inspired to write a story about it. Apparently, Wells was not inspired and neither he nor Langmuir ever published anything about it. After Langmuir and Wells had died, Vonnegut decided to use the idea in his book Cat's Cradle.
- While multiple polymorphs of ice do exist (they can be created under pressure), none has the properties described in this book, and none is stable at standard temperature and pressure above the ordinary melting point of ice. The real Ice IX has none of the properties of Vonnegut's creation, and can exist only at extremely low temperatures and high pressures.
- The ice-nine phenomenon has, in fact, occurred with a few other kinds of crystals, called "disappearing polymorphs". In these cases, a new variant of a crystal has been introduced into an environment, replacing many of the older form crystals with its own form. One example is the anti-AIDS medicine ritonavir, where the newer polymorph destroyed the effectiveness of the drug until improved manufacturing and distribution was developed.
- Ice-nine has been used as a model to explain the infective mechanism of mis-folded proteins called prions which are thought to catalyze the mis-folding of the corresponding normal protein leading to a variety of spongiform encephalopathies such as kuru, scrapie and Creutzfeldt–Jakob disease.
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