The presence of fusel oil in liquors is sometimes quite readily detected, by first removing the ethylic alcohol by gentle evaporation, and then inspecting the odour and taste of the still warm residue. The suspected liquor may also be agitated with an equal volume of ether, water added, and the ethereal stratum removed by means of a pipette, and concentrated by evaporation; the residue is to be examined for amylic alcohol. When distilled with a mixture of sulphuric and acetic acids, amylic alcohol is converted into amylic acetate, which may be recognised by its characteristic pear-like odour; or, the amylic alcohol can be transformed into valerianic acid (which also possesses a distinctive odour) by oxidation with sulphuric acid and potassium dichromate. Another simple qualitative test for fusel oil consists in first decolorising a small quantity of the liquor under examination with animal charcoal, adding a few drops of hydrochloric acid, and then a little freshly distilled and colourless aniline oil, when, in presence of fusel oil, it will be observed that the aniline compound acquires a perceptible rose tint as it falls to the bottom of the liquid. The quantitative determination of fusel oil presents some difficulties. A very ingenious method has been suggested by Marquardt.[118] It consists essentially in first agitating the sample with chloroform, draining off the solution obtained, washing it by repeated shaking with water, and then treating it at 85° with a mixture of 5 parts potassium dichromate, 2 parts sulphuric acid, and 30 parts of water. The valerianic acid thus formed is now separated by distilling the mixture of water and chloroform. The distillate is digested with barium carbonate, next concentrated by evaporation, and then filtered, and divided into two equal portions. One portion is evaporated to dryness, the residue taken up with water containing a little nitric acid, and the amount of barium present determined by precipitation with sulphuric acid. In the other portion, the chlorine originating from a partial oxidation of the chloroform, is to be estimated. The amount of barium combined with the chlorine, is deducted from the total quantity obtained; the remainder represents the proportion in combination with the fatty acids formed by oxidation. Of these, valerianic acid largely predominates; and the amount of barium valerianate [Ba_{2} (C_{2}H_{3}O_{2})] found is calculated to its equivalent in amylic alcohol. Capsicum, creosote, etc., are isolated by treating the sample with ether or benzole, and testing the odour and taste of the evaporated solutions so prepared.