cymogene

from The Century Dictionary.

• noun A mixture of very volatile hydrocarbons found in crude petroleum.
• noun 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.

from the GNU version of the Collaborative International Dictionary of English.

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

from Wiktionary, Creative Commons Attribution/Share-Alike License.

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