FUSEL OIL, the name applied to the volatile oily liquids, of a nauseous fiery taste and smell, which are obtained in the rectification of spirituous liquors made by the fermentation of grain, potatoes, the marc of grapes, and other material, aud which, as they are of higher boiling-point than ethylic alcohol, occur in largest quantity in the last portions of the distillate. Besides ethylic or ordinary alcohol, and amylic or pentylic alcohol, which are present in them all, there have been found in fusel oils several other bodies of the C n H 2n+1 .OH series, also certain ethers, and members of the C s H 2n O 2 series of fatty acids. Normal propylic alcohol, C s H 7 .OH, is contained in the fusel oil of the marc brandy of the south of France, and isoprimary butylic alcohol, CH (CH 3 ) 2 .CHjj.OH, in that of beet-root molasses. The chief constituent of the fusel oil procured in the manufacture of alcohol from potatoes and grain, usually known as fusel oil and potato-spirit, is isoprimary amylic alcohol, or isobutylcarbinol, CH(CH 3 ) 2 .CH 2 .CH 2 .OH, boiling at 129°-130° C., and inactive as regards polarized light. Ordinary fusel oil yields besides another isomeric amylic alcohol, boiling at about 128°, and laevorotatory. The formation of amylic alcohol is stated by Liebig {Familiar Letters on Chemistry, p. 217, 4th ed., 1859) never to take place in fermenting fluids in the presence of tartar, of racemic, tartaric, or citric acid, or of certain bitter substances, as hops. It is produced principally in alkaline or neutral liquids, and in such as contain lactic or acetic acid. Schorlemmer {Proc. Roy. Soc., xv., 1866, p. 131) has shown that amyl-compounds prepared from fusel oil and from American petroleum agree in specific gravity and boiling point, and are therefore to ...