Magnificent Fluorescence of Peppermint Oil.
By PROFESSOR FLÜCKIGER.
50 to 70 drops of peppermint oil shaken with one drop of nitric acid, about 1.2 sp. gr., turn faintly yellowish, brownish, and, after an hour or two, exhibit a most beautiful blue-violet, or greenish-blue color, when examined in transparent light. When observed in reflected light, the liquid is of a copper color, and not transparent. If the mixture is warmed, the green or blue coloration takes place speedily; it may also be immediately provoked by adding a greater amount of nitric acid, say 1 drop to 19, or 9 drops of the essential oil.
Bisulphide of carbon contributes in no way to improve the test. All the various specimens of peppermint oil at my command show the same behavior, but the blue or greenish-blue hue exhibits very appreciable differences, which ought to be further examined by chemists possessing authentic specimens of the oil under notice. A very old specimen of an originally excellent English oil, however, was no longer colored.
The color which peppermint oil thus acquires is remarkable on account of its persistency, for it lasts a week or two, at least in cold. Yet, unfortunately, it appears not capable of being applied as a true test; an admixture of 5 per cent. of oil of turpentine, for instance, does not at all prevent peppermint oil from assuming the blue or green color; on the other hand, I have not as yet met with any other oil partaking of the same behavior; carven, the more volatile portion of caraway-oil, also acquires a slight similar fluorescence, but by no means comparable to the above-described as regards purity and intensity of color.
Peppermint oil, which has become colored in this way, is quickly decolorized if shaken with carbonate of calcium; granulated zinc likewise causes it slowly to turn brownish. Spectroscopic examination of the colored oil furnishes no phenomena of particular interest. Chromic acid, dissolved in chloroform, does not perform the same reaction as nitric acid.—London Pharm. Journ., February 25th, 1871.