cymogene

American Heritage® Dictionary of the English Language, Fourth Edition

1. n. A flammable gaseous fraction of petroleum, consisting chiefly of butane.

Century Dictionary and Cyclopedia

1. n. A mixture of very volatile hydrocarbons found in crude petroleum. When the crude petroleum is distilled, cymogene passes off as a gas at the usual temperature of the condenser, but by low temperature and compression it is reduced to a very volatile liquid having a specific gravity of .603–.578. It is used as a freezing-mixture.
2. n. This very volatile product, obtainable at the beginning of the distillation of crude petroleum, boils under ordinary pressure at 0° C. (32° F.), and consists chiefly of normal butane, C₄H₁₀. Also chymogene.

Wiktionary

1. n. chemistry A highly volatile liquid, condensed by cold and pressure from the first products of the distillation of petroleum; used for producing low temperatures.

GNU Webster's 1913

1. n. (Chem.) A highly volatile liquid, condensed by cold and pressure from the first products of the distillation of petroleum; -- used for producing low temperatures.