Until quite recently we have had no accurate method for the
determination of fusel oil in alcohol or brandy. In 1837 Meurer
suggested a solution of one part of silver nitrate in nine parts of
water as a reagent for its detection, stating that when added to alcohol
containing fusel oil, a reddish brown color is produced, and in case
large quantities are present, a dark brown precipitate is formed. It was
soon found, however, that other substances than amyl alcohol produce
brown colored solutions with silver nitrate; and Bouvier[1] observed
that on adding potassium iodide to alcohol containing fusel oil, the
solution is colored yellow, from the decomposition of the iodide.
Subsequently Boettger[2] proved that potassium iodide is not decomposed
by pure amyl alcohol, and that the decomposition is due to the presence
of acids contained in fusel oil. More accurate results are obtained by
using a very dilute solution of potassium permanganate, which is
decomposed by amyl alcohol much more rapidly than by ethyl alcohol.
[Footnote 1: Zeitschrift f. Anal. Chem. xi., 343.]
[Footnote 2: Dingler's Polytech. Jour., ccxii., 516.]
Depre[3] determines fusel oil by oxidizing a definite quantity of the
alcohol in a closed vessel with potassium bichromate and sulphuric acid.
after removal of excess of the oxidizing reagents, the organic acids are
distilled, and, by repeated fractional distillation, the acetic acid is
separated as completely as possible. The remaining acids are saturated
with barium hydroxide, and the salts analyzed; a difference between the
percentage of barium found and that of barium in barium acetate proves
the presence of fusel oil, and the amount of difference gives some idea
of its quantity. Betelli[4] dilutes 5 c.c. of the alcohol to be tested
with 6 to 7 volumes of water, and adds 15 to 20 drops of chloroform and
shakes thoroughly. If fusel oil is present, its odor may be detected by
evaporating the chloroform; or, by treatment with sulphuric acid and
sodium acetate, the ether is obtained, which can be readily recognized.
Jorissen[5] tests for fusel oil by adding 10 drops of colorless aniline
and 2 to 3 drops of hydrochloric acid to 10 c.c. of the alcohol. In the
presence of fusel oil a red color is produced within a short time, which
can be detected when not more than 0.1 per cent. is present. But
Foerster[6] objects to this method because he finds the color to be due
to the presence of furfurol, and that pure amyl alcohol gives no color
with aniline and hydrochloric acid.
[Footnote 3: Pharm. J. Trans. [3] vi., 867.]
[Footnote 4: Berichte d. Deutschen Chem. Gesellsch., viii., 72.]
[Footnote 5: Pharm. Centralhalle, xxii., 3.]
[Footnote 6: Berichte d. Deutsch. Chem. Gesellsch., xv., 230.]
Hager[7] detects fusel oil as follows: If the spirit contains more than
60 per cent. of alcohol, it is diluted with an equal volume of water and
some glycerine added, pieces of filter paper are then saturated with the
liquid and exposed to the After the evaporation of the alcohol, the odor
of the fusel oil can be readily detected. For the quantitative
determination he distills 100 c.c. of the alcohol in a flask of 150 to
200 c.c. capacity connected with a condenser, and so arranged that the
apparatus does not extend more than 20 cm. above the water bath. This
arrangement prevents the fusel oil from passing over. If the alcohol is
stronger than 70 per cent., and the height of the distillation apparatus
is not more than 17 cm., the residue in the flask may be weighed as
fusel oil. With a weaker alcohol, or an apparatus which projects further
out of the water bath, the residual fusel oil is mixed with water. It
can, however, be separated by adding strong alcohol and redistilling, or
by treating with ether, which dissolves the amyl alcohol, and
distilling, the temperature being raised finally to 60 deg..
[Footnote 7: Pharm. Centralhalle, xxii., 236.]
Marquardt,[8] like Betelli, extracts the fusel oil from alcohol by means
of chloroform, and by oxidation converts it into valeric acid. From the
quantity of barium valerate found he calculates the amount of amyl
alcohol present in the original solution; 150 c.c. of the spirit, which
has been diluted so as to contain 12 to 15 per cent. of alcohol, are
shaken up thoroughly with 50 c.c. of chloroform, the aqueous layer drawn
off, and shaken with a fresh portion of chloroform. This treatment is
repeated several times. The extracts are then united, and washed
repeatedly with water. The chloroform, which is now free from alcohol
and contains all the fusel oil, is treated with a solution of 5 grammes
of potassium bichromate in 30 grammes of water and 2 grammes of
sulphuric acid, and then heated in a closed flask for six hours on a
water bath at 85 deg.. The contents of the flask are then distilled, the
distillate saturated with barium carbonate, and the chloroform
distilled; the residue is evaporated to a small volume, the excess of
barium carbonate filtered off, and the filtrate evaporated to dryness
and weighed. The residue is dissolved in water, a few drops of nitric
acid added, and the solution divided into two portions. In the first
portion the barium is determined; in the second the barium chloride. The
total per cent. of barium minus that of barium chloride gives the amount
present as barium valerate, from which is calculated the per cent. of
amyl alcohol. By this process the author has determined one part of
fusel oil in ten thousand of alcohol. To detect very minute quantities
of fusel oil, the chloroform extracts are treated with several drops of
sulphuric acid and enough potassium permanganate to keep the solution
red for twenty-four hours. If allowed to stand in a test tube, the odor
of valeric aldehyde will first be noticed, then that of amyl valerate,
and lastly that of valeric acid.--_Amer. Chem. Journal._
[Footnote 8: Berichte d. Deutsch. Chem. Gesellsch., xv., 1,370
and 1,663.]
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