This section is from the book "A Treatise On Beverages or The Complete Practical Bottler", by Charles Herman Sulz. Also available from Amazon: A Treatise On Beverages.
The oil of fennel is obtained from the fennel-fruit of Southern and Western Europe, frequently found wild, extensively cultivated in Germany and France. By distilling the bruised fennel seed with water or by means of superheated steam a colorless or yellowish oil of agreeable fennel odor,sweetish aromatic taste (oil of sweet fennel) is obtained, yielding about three and one-half to four per cent. Its specific gravity is 0.960 to 0.990 (not less than 0.960, IT. S. P. G.); it congeals below 10° C. (50° F.), "sometimes not until cooled below the freezing point of water" (N. D.). Zeller obtained an oil which remained liquid at - 20° C. (- 4° F.). The congealing point of the oil becomes lower by age. Oil of fennsl is soluble in alcohol in all proportions.
The solution in alcohol should not become dark-colored on the addition of a little ferric chloride (phenol, etc.). One drop of the oil, triturated with sugar and afterward with one pint of water, should impart to the latter the pure flavor of fennel (other volatile oils). - P. G.