[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°. 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,