• Webster's Revised Unabridged Dictionary
    • n Cymogene (Chem) A highly volatile liquid, condensed by cold and pressure from the first products of the distillation of petroleum; -- used for producing low temperatures.
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Century Dictionary and Cyclopedia
    • n cymogene 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.
    • n cymogene 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.
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In literature:

Different varieties are sold under the names of cymogene, gasolene, naphtha, petrol, and benzoline.
"Aids to Forensic Medicine and Toxicology" by W. G. Aitchison Robertson
The lightest of all, cymogene, is given off even at the freezing-point of water.
"Marvels of Scientific Invention" by Thomas W. Corbin