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• n  a colorless volatile highly flammable liquid obtained from petroleum and used as an anesthetic or a solvent or in determining octane ratings

• According to the announcement, the committee proceeded by selecting two chemicals, one knock-preventing (iso-octane), one knock-producing (normal heptane).
• An identical motor is then run on various mixtures of 1) heptane (a bad knocker) and 2) isooctane (once thought to be the perfect knockless fuel) until its knocking corresponds .