PEPPERMINT, an indigenous perennial herb of the natural order Labiatx, and genus Mentlia, the specific name being Mentha Piperita, Huds., 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 Continent, and is also extensively cultivated for the sake of its essential oil in England, in several parts of continental Europe, and in the United States. Yet it was 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 Britannicarum (1696). The medicinal properties of the plant were speedily recog-nized, and it was admitted into the London Bharmacopoeia in 1721, under the name of Mentha piperitis sapore.
Two varieties are recognized by growers, the one being known as white and the other as black mint. The former has purplish and the latter green stems; the leaves are more coarsely serrated in the white. The black is the variety more generally culti-vated, probably because it is found to yield more oil, but that of the green variety is considered to have a more delicate odour, and obtains a higher price. The green is the kind chiefly dried for herbalists ;
it is said to be
Yia. l.MeiUha Piperita, a, Flowering branch;
of less Vigorous t>, flower showing form of calyx teeth.
growth than the black. The annual yield of peppermint oil from all parts of the world has been estimated at 90,000 lb, but this is probably much below the mark, without taking into consideration the Chinese and Japan-ese oils of peppermint, which, however, are obtained from a different species of mint.
Peppermint oil varies considerably in commercial value, that of Mitcham commanding nearly three times the price of the finest American. The flavour varies to a slight extent even with particular plots of land, badly drained ground being known to give unfavourable results both as to the quantity and quality of the oil. That of the Japan-ese and Chinese oil also differs slightly from the English, and is thus distinguishable by experts. In America the oil is liable to be injured in flavour by aromatic weeds which grow freely among the crop, the most troublesome of these being Brigeron canadense, L., and Erechthites hieracifolia, Raf. 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. It has a specific gravity of 0'84 to 0-92, and boils at 365° Fahr. Mitcham oil, when examined by polarized light in a column 50 mm. long, deviates from 14°-2 to 10°'7 to the left, the American 4*-3. When oil of peppermint is cooled to 4° C. it sometimes deposits colourless hexagonal prisms of menthol, C10H20O, which are soluble in alcohol and ether, almost insoluble in water, and fusible at 92° Fahr. The liquid portion of the oil appears to consist chiefly of the compound C10H18O, but it has not been thoroughly investigated. Oil of peppermint is often adul-terated with a third part of rectified spirit, which may be detected by the milkiness produced when the oil is agitated with water. Oil of rosemary and rectified oil of turpen-tine are sometimes used for the same purpose. If the oil contains turpentine it will explode with iodine. If quite pure it dissolves in its own weight of rectified spirits of wine. Peppermint oil is largely distilled at Canton, a considerable quantity (about 300 catties annually) being sent to Bombay, also about 600 catties of menthol. The exports from Canton in 1883 amounted to about 1200 lb. The species cultivated in the neighbourhood of Canton, and probably at Shanghai also, is Mentha arvensis, var. glabrata. Peppermint is chiefly culti-vated in the province of Keang-se; and according to native statements as much as 40 piculs of oil of peppermint are sent annually to ports on the coast. In Japan also the distillation of oil of pepper-mint forms a considerable industry, the plant cultivated being M. arvensis, var. piper-ascens (see Ph. Journ.  vol. ii. p. 324), of which both a purplish and a white form appear to be grown. The oil, under the name of hakha no abura, is exported from Hiogo and Ozaka, but is said to be frequently adulterated. Since 1872 the peppermint camphor or menthol has been largely exported in the separate state from Japan to Germany and Great Britain. The menthol is obtained by subjecting 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. It is re-markable, however, that the M. arvensis, var. javanica, Blume, growing in Ceylon, has not the flavour of pepper-mint but that of garden mint, while the typical form of M. arvensis grown in Great Britain has an odour so different from'peppermint that it has to be carefully re-moved from the field lest it should spoil the flavour of the peppermint oil when the herb is distilled. M. incana, Willd., cultivated near Bombay as a herb, also possesses the flavour of peppermint. In the form in which menthol is imported it bears some resemblance to Epsom salts, with which it is said to be sometimes adulterated. It is usually not entirely free from the essential oil, and consequently undergoes purification and recrystallization in England and on the Continent. The amount of menthol imported by a large firm at Leipsic between September 1883 and April 1884 is stated by them to have been 6380 lb, while it is certain that at least an equal quantity is imported into England from Yokohama. Although the Japanese pepper-mint plant has been imported by a London merchant, no attempt has as yet been made to cultivate the plant in order to manufacture menthol in England. Menthol is now (1884), however, tnanufactured from M. Piperita in the United States, where also M. arvensis, var. piperascens, is cultivated.
Oil of peppermint is used in medicine as an antispasmodic for the relief of griping pains in the alimentary canal, to expel flatulence, to relieve nausea, to hide the taste of other medicines, and to act as an adjunct to purgatives. The dose is usually from one to three minims. It forms a most valuable remedy in diarrhoea, acting as an antiseptic, and as a stimulant to the circulation, and as an anodyne. The oil rubbed over the head is used in China to cure sun-stroke. Menthol has lately come largely into use as a remedy for neuralgia, being moulded by heat into the form of small cones, which are rubbed over the part affected. A small portion placed on the tongue frequently relieves headache, and catarrh and coryza if placed in the nostril. The largest consumption of the oil is in the manufacture of peppermint lozenges.
The following mode of cultivation is adopted by Mr Holland, at. Market Deeping. A rich friable soil, retentive of moisture, is selected, and the ground is well tilled 8 to 10 inches deep. The plants are propagated in the spring, usually in April and May. When the young shoots from the crop of the previous year have attained a height of about 4 inches they are pulled up and trans-planted into new soil. They grow vigorously the first year, and throw out numerous stolons on the surface of the ground. After the crop has been removed these are allowed to harden or become woody, and then farmyard manure is scattered over the field and ploughed in. In this way the stolons are divided into numerous pieces, and covered with soil before the frost sets in. If the autumn is wet they are liable to become sodden, and rot, and the next crop fails. In the spring the fields are dressed with Peruvian guano. In new ground the peppermint requires hand-weeding two or three times, as the hoe cannot be used without injury to the plants. Moist heavy weather in August is apt to cause the foliage to drop off and leave the stems almost bare. Under these circum-stances rust (Puecinia Menihse) also is liable to attack the plants. This is prevented to a certain extent by a rope being drawn across the plants, by two men walking in the furrows, so as to remove excessive moisture. The average yield of peppermint is about 165 cwt. per acre. The first year's crop is always cut wdth the sickle to prevent injury to the stolons. The herb of the second and third year is cut with scythes, and then raked by women into loose heaps ready for carting. The field is then gleaned by boys, who add what they collect to the heaps. The plants rarely yield a fourth crop on the same land. The harvest usually commences in the beginning or middle of August, or as soon as the plants begin to flower, and lasts for six weeks, the stills being kept going night and day. The herb is carted direct from the field to the stills, which are made of copper, and contain about 5 cwt. of the herb. Before putting the peppermint into the still water is poured in to a depth of about 2 feet, at which height a false bottom is placed, and on this the herb is thrown and trodden down by men. The lid, which fits into a water-joint, is then let down by pulleys and fastened by two bars, any excess of pressure or temperature being indicated by the water that is ejected at the joint. The distillation is conducted by the application of direct heat at the lowest pos-sible temperature, and is continued for about four and a half hours. When this operation is completed, the lid is removed and a rope is attached to a hook on the false bottom, which, as well as the herb resting on it, is raised bodily by a windlass and the peppermint carried away in the empty carts on their return journey to the fields, where it is placed in heaps and allowed to rot, being subsequently mixed with the manure applied in the autumn as above stated.
At Mitcham extra payment is given to the reapers to induce them to keep the mint free from corn mint (Mentha arvensis) and other herbs, which would injure or spoil the flavour of the oil if not removed before distillation. The usual yield of oil, if the season be warm and dry, is said to be 1 oz. from 5 lb of the fresh flowering herb, but, if wet and unfavourable, the product is barely half that quantity. Mr Holland estimates the yield of a charge of the still at from 1 lb 12 oz. to 5 lb. The oil improves in mellow-ness even if kept as long as ten or fourteen years. The green colour sometimes present in the oil is stated to be due to a quantity of water larger than necessary having been used in the distillation ; on the other hand, if the herb be left in the still from Saturday to Monday, the oil assumes a brown tint.
In France peppermint is cultivated on damp rich ground at Sens, in the department of the Yonne. In Germany it is grown in the neighbourhood of Leipsic, where the little town of Colleda produces annually as much as 40,000 cwt. of the herb. In the United States peppermint is cultivated on a most extensive scale, chiefly in southern Michigan, the west districts of New York State, and Ohio. The amount of peppermint oil now produced fn the United States has been estimated at 70,000 lb annually, of which 30,000 ft> are exported, about two-thirds of this quantity being produced in New York State and the remaining one-third in Michigan. The yield averages from 10 to 30 lb per acre. The cultivation of pepper-mint has recently been extended to the southern States. In Michi-gan the plant was introduced in 1855, and in 1858 there were about '2100 acres under cultivation, and 100 distilleries yielding 15,000 lb of oil. In 1870 one of the best-known growers of New York State is said to have sent out as much as 57,365 fb. In 1876 the United States exported to Hamburg 25,840 lb of peppermint oil against 14,890 lb sent by Great Britain to the same port. (E. M. H.)
Near Mitcham in Surrey (219 acres in 1864), Wisheach in Cam-bridgeshire, Market Deeping in Lincolnshire (150 acres in 1881), and Hitchin in Hertfordshire.
The above article was written by: E. M. Holmes, F.L.S., Curator of Museum, Pharmaceutical Society, London.