Part 2

. (1568) 54.

=Chemical Composition=—Spearmint yields an essential oil (_Oleum Menthæ viridis_) in which reside the medicinal virtues of the plant. Kane,[1759] who examined it, gives its sp. gr. as 0·914, and its boiling point as 160° C. The oil yielded him a considerable amount of stearoptene. Gladstone[1760] found spearmint oil to contain a hydrocarbon almost identical with oil of turpentine in odour and other physical properties, mixed with an oxidized oil to which is due the peculiar smell of the plant. The latter oil boils at 225° C.; its sp. gr. is 0·951, and it was found to be isomeric with carvol, C₁₀H₁₄O. According to our experiments the oil, distilled from Curled Mint grown in Germany, deviates the plane of polarization 37°·4 to the left when examined in a column of 100 millimetres. We prepared from it the crystallized compound (C₁₀H₁₄0)₂SH₂, and isolated from it the liquid C₁₀H₁₄O, which differs from carvol (see Fructus Carui, page 306) by its levogyrate power.[1761]

=Uses=—Spearmint is used in the form of essential oil and distilled water, precisely in the same manner as peppermint In the United States the oil is also employed by confectioners and the manufacturers of perfumed soap.

=Substitutes=—Oil of spearmint is now rarely distilled in England, its high cost[1762] causing it to be nearly unsaleable. The cheaper foreign oil is offered in price-currents as of two kinds, namely _American_ and _German_. Of the first we have already spoken: the second, termed in German _Krauseminzöl_, is the produce of _Mentha aquatica_ L. var. γ _crispa_ Bentham, a plant cultivated in Northern Germany. Its oil seems to agree with the oil of spearmint.

HERBA MENTHÆ PIPERITÆ.

_Peppermint_; F. _Menthe poivrée_; G. _Pfefferminze_.

=Botanical Origin=—_Mentha piperita_ Hudson (non Linn.), an erect usually glabrous perennial, much resembling the Common Spearmint of the gardens, but differing from it in having the leaves all stalked, the flowers larger, the upper whorls of flowers somewhat crowded together, and the lower separate. In the opinion of Bentham it is possibly a mere variety of _M. hirsuta_ L., with which it can be connected by numerous intermediate forms.

Peppermint rapidly propagates itself by runners, and is now found in wet places in several parts of England, as well as on the Continent. It is cultivated on the large scale in England, France, Germany, and North America.

=History=—_Mentha piperita_ was first observed in Hertfordshire by Dr. Eales, and communicated to Ray, who in the second edition of his _Synopsis Stirpium Britannicarum_, 1696, noticed it under the name of _Mentha spicis brevioribus et habitioribus, foliis Menthæ fuscæ, sapore fervido piperis_; and in his _Historia Plantarum_[1763] as “_Mentha palustris_ ... _Peper-Mint_.”[1764] Dale, who found the plant in the adjoining county of Essex, states[1765] that it is esteemed a specific in renal and vesical calculus; and Ray, in the third edition of his _Synopsis_, declares it superior to all other mints as a remedy for weakness of the stomach and for diarrhœa. Peppermint was admitted to the London Pharmacopœia in 1721, under the designation of _Mentha piperitis sapore_.

[1759] _Philosophical Magazine_, xiii. (1838) 444.

[1760] _Journ. of Chemical Society_, ii. (1854) 11.

[1761] Flückiger, _Pharm. Journ._ vii. (1876) 75.

[1762] Price from 1824 to 1839, 40_s._ to 48_s._ per lb.

[1763] Tomus iii. (1704) 284.

[1764] I have examined the original specimen still preserved among Ray’s plants in the British Museum and find it to agree perfectly with the plant now in cultivation.—D. H.

[1765] _Pharmacologiæ Supplementum_, Lond. 1705. 117.

The cultivation of peppermint at Mitcham in Surrey dates from about 1750,[1766] at which period only a few acres of ground were there devoted to medicinal plants. At the end of the last century, above 100 acres were cropped with peppermint. But so late as 1805 there were no stills at Mitcham, and the herb had to be carried to London for the extraction of the oil. Of late years the cultivation has diminished in extent, by reason of the increased value of land and the competition of foreign oil of peppermint.

On the Continent Mentha Piperitis was grown as early as 1771 at Utrecht; Gaubius[1767] appears to have been the first to notice “_Camphora Europæa Menthæ Piperitidis_,” i.e. Menthol (see page 483).

In Germany peppermint became practically known in the latter half of the last century, especially through the recommendation of Knigge.[1768]

=Description=—The rootstock of peppermint is perennial, throwing out runners. The stem is erect, 3 to 4 feet high, when luxuriant somewhat branched below with erecto-patent branches, firm, quadrangular, slightly hairy, often tinged with purple. Leaves all stalked, the stalks of the lower ½ to ¾ of an inch long, naked or nearly so, the leaf lanceolate, narrowed or rather rounded towards the base, the point narrowed out and acute, the lowest 2 to 3 inches long by about ¾ of an inch broad, naked and dull green above, paler and glandular all over, but only slightly hairy upon the veins beneath; the teeth sharp, fine, and erecto-patent. Inflorescence in a loose lanceolate or acutely conical spike, 2 to 3 inches long by about ¾ of an inch broad at the base, the lowest whorls separate, and usually the lowest bracts leaf-like. Bracteoles lanceolate-acuminate, about equalling the expanded flowers, slightly ciliated. Pedicels 1 to 1½ lines long, purplish, glandular but not hairy. Calyx often purplish, the tube about 1 line long and the teeth ½ a line, the tube campanulate-cylindrical, purplish, not hairy, but dotted over with prominent glands; the teeth lanceolate subulate, furnished with short erecto-patent hairs. Corolla reddish-purple about twice as long as the calyx, naked both within and without. Nut smooth[1769] (_rugose_, according to our observation). The odour and taste are strongly aromatic.

In var. 2. _vulgaris_ of Sole, _M. piperita_ β. Smith, the plant is more hairy, with the spikes broader and shorter, or even bluntly capitate. colourless, pale yellow, or greenish liquid, of sp. gr. varying from 0·84 to 0·92. We learn from information kindly supplied by Messrs. Schimmel and Co., Leipzig, that the best peppermint grown in Germany, carefully dried, affords from 1 to 1·25 per cent. of oil. It has a strong and agreeable odour, with a powerful aromatic taste, followed by a sensation of cold when air is drawn into the mouth. We find that the Mitcham oil examined by polarized light in a column 50 mm. long, deviates from 14°·2 to 10°·7 to the left, American oil 4°·3.

=Chemical Composition=—The constituent for the sake of which peppermint is cultivated is the essential oil, _Oleum Menthæ piperitæ_, a coloureless, pale yellow or greenish liquid, of sp. gr. varying from 0·84 to 0·92. We learn from information kindly supplied by Messrs. Schimmel and Co., Leipzig, that the best peppermint grown in Germany, carefully dried from 1 to 1·25 per cent of oil. It has a strong and agreeable odour, with a powerful aromatic taste, followed by a sensation of cold when air is drawn into the mouth. We find that the Mitcham oil examined by polarized light in a column 50 mm. long, deviates from 14·2° to 10·7° to the left, American oil 4·2°.

[1766] Lysons, _Environs of London_, i. (1800) 254.

[1767] _Adversariorum varii argumenti liber unus_, Leidae, 1771. 99.

[1768] _De Menthâ Piperitide Commentatio_, Erlangæ, 1780.

[1769] This description is borrowed from Mr. Baker’s paper on the English Mints, referred to at page 480, note 1.

When oil of peppermint is cooled to -4° C., it sometimes deposits colourless hexagonal crystals of _Peppermint Camphor_, C₁₀H₁₉OH, called also _Menthol_. We have never observed it, nor are we aware that menthol has been noticed in America, but it is largely afforded by eastern mints, and found in commerce under the name of _Chinese_ or _Japanese Oil of Peppermint_,[1770] either liquid, and easily depositing the camphor, or also forming a crystalline mass impregnated with the liquid oil.

Pure menthol has the exquisite odour and taste of peppermint; it forms hexagonal crystals, melting at 42° C., and boiling at 212° C. By distilling menthol with P₂O₅ it yields menthene, C₁₀H₁₈, a levogyrate liquid, boiling at 163°, the peculiar odour of which reminds of peppermint.[1771] The Chinese crystallized oil of peppermint has sometimes a bitterish after-taste and an odour similar to that of spearmint, but by recrystallization it assumes the pure flavour.

The liquid part of the oil of peppermint has not yet been thoroughly investigated; it appears to consist chiefly of the compound C₁₀H₁₈O. Upon the liquid portions depend the remarkable colorations which the oil of peppermint is capable of assuming. If 50 to 70 drops of the crude oil are shaken with one drop of nitric acid, sp. gr. about 1·2, the mixture changes from faintly yellowish to brownish, and, after an hour or two, exhibits a bluish, violet or greenish colour; in reflected light, it appears reddish and not transparent. The colour thus produced lasts a fortnight. We have thus examined the various samples of peppermint oil at our command, and may state that the finest among them assume the most beautiful coloration and fluorescence, which, however, shows very appreciable differences. An inferior oil of American origin was not coloured; and a very old sample of an originally excellent English oil was likewise not coloured by the test. Menthol is not altered when similarly treated.[1772] The nitric acid test is not capable of revealing adulterations of peppermint oil, for the coloration takes place with an oil to which a considerable quantity of oil of turpentine has been added.

[1770] The Chinese oil is distilled at Canton, and was exported from Canton in 1872 to the extent of 800 lbs.; it was valued at about 30s. per lb.—See also Flückiger in _Pharm. Journ._ Oct. 14, 1871. 321. As to Japan we are informed that there are large plantations of peppermint; the oil “Hakano Abura” is exported from Hiogo and Osaka, but frequently adulterated. Mr. Holmes informed me (1879) that he found the mother plant coming nearest to _Mentha canadensis_.—F. A. F..

[1771] On Japanese Peppermint Camphor see Beckett and Alder Wright, _Yearbook of Pharm._ 1875. 605.

[1772] _Pharm. Journ._ Feb. 25, 1871. 682.

Remarkable colorations of a different hue are also displayed by the various kinds of oil of peppermint if other chemical agents are mixed with it. Thus green or brownish tints are produced by means of _anhydrous_ chloral; the oil becomes bluish or greenish or rose-coloured if shaken with a concentrated solution of bisulphite of sodium. It is worthy of note that oils of different origin, which cannot be distinguished by means of nitric acid, exhibit totally different colorations if mixed with either of the liquids just named, or with vapour of bromine. This behaviour may be of some use in the examination of commercial sorts of peppermint oil.

As to bisulphite of sodium, it yields a solid compound with certain kinds of peppermint oil, which we have not yet examined.

=Production and Commerce=—In several parts of Europe, as well as in the United States, peppermint is cultivated on the large scale as a medicinal plant.

In England the culture is carried on in the neighbourhood of Mitcham in Surrey, near Wisebeach in Cambridgeshire, Market Deeping in Lincolnshire, and Hitchin in Hertfordshire.

At Mitcham in 1850 there were about 500 acres under cultivation; in 1864 only about 219 acres.[1773] At Market Deeping there were in 1871 about 150 acres cropped with peppermint. The usual produce in oil may be reckoned at 8 to 12 lb. per acre. The fields of peppermint at Mitcham are level, with a rich, friable soil, well manured and naturally retentive of moisture. The ground is kept free from weeds, and in other respects is carefully tilled. The crop is cut in August, and the herb is usually allowed to dry on the ground before it is consigned to the stills. These are of large size, holding 1000 to 2000 gallons, and heated by coal; each still is furnished with a condensing worm of the usual character, which passes out into a small iron cage secured by a padlock, in which stands the oil separator. The distillation is conducted at the lowest possible temperature. The water that comes over with the oil is not distilled with another lot of herb, but is for the most part allowed to run away, a very little only being reserved as a perquisite of the workmen. The produce is very variable, and no facilities exist for estimating it with accuracy.[1774] It is however stated that a ton of dried peppermint yields from 2½ to 3½ pounds of oil, which equals 0·11 to 0·15 per cent. But we have been assured by a grower at Mitcham that the yield is as much as 6 pounds from a ton, or 0·26 per cent.

At Mitcham and its neighbourhood two varieties of peppermint are at present recognized, the one being known as _White Mint_, the other as _Black Mint_, but the differences between the two are very slight. The Black Mint has _purple_ stems; the White Mint, _green_ stems, and as we have observed, leaves rather more coarsely serrated than those of the Black. The Black Mint is more prolific in essential oil than the White, and hence more generally cultivated; but the oil of the latter is superior in delicacy of odour and commands a higher price. White Mint is said to be principally grown for drying in bundles, or as it is termed “_bunching_.”

[1773] _Pharm. Journ._ x. (1851) 297. 340; also Warren in _Pharm. Journ._ vi. (1865) 257. To these papers and to personal inquiries we are indebted for most of the particulars relating to peppermint culture at Mitcham.

[1774] Only the larger growers have stills. These they let to smaller cultivators who pay so much for distilling a charge, _i.e._ whatever the still can be made to contain, without reference to weight. Hence the dried herb is preferred to the fresh, as a larger quantity can be distilled at one time.

Peppermint is grown on a vastly larger scale in America, the localities where the cultivation is carried on being Southern Michigan, Western New York, and Ohio. In Michigan where the plant was introduced in 1855, there were in 1858 about 2100 acres devoted to its growth, all with the exception of about 100 acres being in the county of St. Joseph, where there are about 100 distilleries. The average produce of this district was estimated in 1858 at 15,000 lb.; but the yield fluctuates enormously, and in the exceptionally fine season of 1855 it was reckoned at 30,000 lb. We must suppose that it is sometimes much larger, for we have been informed by Mr. H. G. Hotchkiss, of Lyons, Wayne County, State of New York, one of the most well-known dealers, in a letter under date Oct. 10, 1871, that the quantity sent out by him in the previous year reached the enormous amount of 57,365 lb. It is further stated by the official statistics of Hamburg for the year 1876 that this port received 25,840 lb. of peppermint oil from the United States and 14,890 lb. from Great Britain.

From the statistics quoted by Stearns[1775] it would appear that the produce of oil per acre is somewhat higher in America than in England, but from various causes information on this head cannot be very reliable.

Peppermint is cultivated at Sens in the department of the Yonne in France[1776] and in Germany in the environs of Leipzig, where the little town of Cölleda produces annually as much as 40,000 cwts. of the herb.

The annual crop of the world is supposed to yield 90,000 lb. of peppermint oil.[1777]

Peppermint oil varies greatly in commercial value, that of Mitcham commanding twice or three times as high a price as the finest American. Even the oil of Mitcham is by no means uniform in quality, certain plots of ground affording a product of superior fragrance. A damp situation or badly drained ground is well known to be unfavourable to the quantity and quality of oil.

The presence of weeds among the peppermint is an important cause of deterioration to the oil, and at Mitcham some growers give a gratuity to their labourers to induce them to be careful in throwing out other plants when cutting the herb for distillation. One grower of peppermint known to us was compelled to abandon the cultivation, owing to the enormous increase of _Mentha arvensis_ L. which could not be separated, and which when distilled with the peppermint ruined the flavour of the latter. In America great detriment is occasioned by the growth of _Erigeron canadensis_ L. Newly cleared ground planted with peppermint is liable to the intrusion of another plant of the order Compositæ, _Erechtites hieracifolia_ Raf., which is also highly injurious to the quality of the oil.[1778]

=Uses=—A watery or spirituous solution of oil of peppermint is a grateful stimulant, and is a frequent adjunct to other medicines. Oil of peppermint is extensively consumed for flavouring and cordials.

[1775] To whose paper _On the Peppermint Plantations of Michigan_ in the _Proceedings of the Americ. Pharm. Assoc._ for 1858, we owe the few particulars for which we can here afford space.—To be farther consulted, same _Proceedings_, 1876. 828.

[1776] _Journ. de Pharm._ viii. (1868) 130.—Abstract from Roze, _La Menthe poivrée, sa culture en France, ses produits, falsifications de l’essence et moyens de les reconnaître_, Paris, 1868. 43 pages.

[1777] Todd, _Proceedings Am. Ph. Ass._ 1876, 828.

[1778] Maisch, _American Journ. of Pharm._ March 1870. 120.

HERBA PULEGII.

_Pennyroyal_[1779]; F. _Menthe pouliot_, _Pouliot vulgaire_; G. _Polei_.

=Botanical Origin=—_Mentha Pulegium_ L., a small perennial aromatic plant, common throughout the south of Europe and extending northward to Sweden, Denmark, England and Ireland, eastward to Asia Minor and Persia, and southward to Abyssinia, Algeria, Madeira and Teneriffe. It has been introduced into North[1780] and South America. For medicinal use it is cultivated on a small scale.

=History=—Pennyroyal was in high repute among the ancients. Both Dioscorides and Pliny describe its numerous virtues. In Northern Europe it was also much esteemed, as may be inferred from the frequent reference to it in the Anglo-Saxon and Welsh works on medicine.

Gerarde considered the plant to be “so exceedingly well known to all our English nation” that it needed no description. In his time (_circa_ 1590), it used to be collected on the commons round London, whence it was brought in plenty to the London markets. At the present day pennyroyal has fallen into neglect, and is not named in the British Pharmacopœia of 1867.

=Description=—The plant has a low, decumbent, branching stem, which in flowering rises to a height of about 6 inches. Its leaves, scarcely an inch in length and often much less, are petiolate, ovate, blunt, crenate at the margin, dotted with oil-glands above and below. The flowers are arranged in a series of dense, globose whorls, extending for a considerable distance up the stem. The whole plant is more or less hairy. It has a strong fragrant odour, less agreeable to most persons than that of peppermint or spearmint. Its taste, well perceived in the distilled water, is highly aromatic.

=Chemical Composition=—The most important constituent of pennyroyal is the essential oil, known in pharmacy as _Oleum Pulegii_, to which is due the odour of the plant. It has been examined by Kane,[1781] according to whom it has a sp. gr. of 0·927. Its boiling was found to fluctuate between 183° and 188° C. The formula assigned to it by this chemist is C₁₀H₁₆O. We ascertained that it contains no carvol (see page 481.)

=Production=—Pennyroyal is cultivated at Mitcham and is mostly sold dried; occasionally the herb is distilled for essential oil. The oil found in commerce is however chiefly French or German, and far less costly than that produced in England.

=Uses=—The distilled water of pennyroyal is carminative and antispasmodic, and is used in the same manner as peppermint water.

[1779] _Pennyroyal_, in old herbals _Puloil royal_ is derived from _Puleium regium_, an old Latin name given from the supposed efficacy of the plant in destroying fleas (Prior).

[1780] The native Pennyroyal is however a different plant, namely _Hedeoma pulegioides_ Pers., figured in