PEPPERMINT, an indigenous perennial herb of the family Labiatae, and genus Mentlia (see MINT), the specific name being 111entha piperita, is distinguished from other species of the genus by its stalked leaves and oblong-obtuse spike-like heads of flowers. It is met with, near streams and in wet places, in several parts of England and on the European continent, where—as also in the United States—it is cultivated for the sake of its essential oil. It was, however, only recognized as a distinct species late in the 17th century, when Dr. Eales discovered it in Hertfordshire and pointed it out to Ray, who published it in the second edition of his Synopsis stirpium britannicaruen (1696). The medicinal properties of the plant were speedily recognized and it was ad mitted into the London Pharmacopoeia in 1721, under the name of Ilentha piperitis sapore.
Two varieties are recognized by growers, the white and the black mint. The former has purplish and the latter green stems; the leaves are more coarsely serrated in the white. The black is more generally cultivated, probably because it is found to yield more oil, but that of the white variety is considered to have a more delicate odour, and obtains a higher price. The white is the kind chiefly dried for herbalists. When pure the oil is nearly colourless and has an agreeable odour and powerful aromatic taste, followed by a sensation of cold when air is drawn into the mouth. When oil of peppermint is cooled to 4° C it sometimes deposits colourless hexagonal prisms of menthol, C10H200, which are soluble in alcohol and ether, almost insoluble in water, and fusible at 92° F ; the oil consists chiefly of menthol and a terpene called menthene, Oil of peppermint is often adulterated with a third part of rectified spirit, which may be detected by the milkiness produced when it is agitated with water. Oil of rosemary and rectified oil of turpentine are sometimes used for the same purpose.
Peppermint oil is largely distilled at Canton, a considerable quantity being sent to Bombay, also a large quantity of menthol. The species cultivated in the neighbourhood of Canton, is Mentha arvensis, var. glabrata. In Japan also the distillation of o:1 of peppermint forms a considerable industry, the plant cultivated being M. arvensis, var. piperascens. The oil, under the name of hakka no abura, is exported from Hiogo and Ozaka, but is said to be frequently adulterated. The menthol is obtained by sub jecting the oil to a low temperature, when it crystallizes out and is separated. The two varieties of M. arvensis just named yield much more menthol than M. piperita.
Since about 190o the United States has been an important pro ducer of peppermint oil. Production on a large commercial scale was first attained in southern Michigan. Shortly after the World War peppermint culture was extended to northern Indiana, the two States producing in 1925 more than three-fourths of the world's supply of true peppermint oil.
The volatile oil of Mentha piperita is a valuable and widely used drug. Its chief constituents are menthol and menthene, which is a liquid terpene. The British Pharmacopoeia contains two preparations of this oil, the Aqua menthae piperitae and the Spiritus menthae piperitae. The oil has the characters of its class, with certain special features. Its local anaesthetic action is exceptionally strong, and is also powerfully antiseptic. These properties make it valuable in the relief of toothache and also in certain forms of dyspepsia and in colic generally, "soda-mint lozenges" being a familiar form. The characteristic anti-spas modic action of the volatile oils is perhaps more marked in this than in any other oil, and greatly adds to its power of relieving pains arising in the alimentary canal.