ESSENTIAL OILS ISOMERIC WITH OIL OF TURPENTINE.

587

amongst which the principal is the hydrocarbon Є0H16, which may be isolated by repeated fractionated distillation.

5. Essence of Camomile: of this there are two varieties, one of which is obtained from the Anthemis nobilis; it is of a greenish colour, and consists of a hydrocarbon (E10H16), and an oxidized portion (ЄH?), which when heated with caustic potash is converted into potassic angelate (KЄH,O), with evolution of hydrogen (1296). The second variety is obtained from the Matricaria chamomilla. It is remarkable for its deep blue colour : it contains an oxidized oil (HO), which has the composition of laurel camphor. It may be distilled without change, and remains liquid below 32°.

10 16

The oil of the Achillea millefolium is also distinguished by its beautiful blue colour, but it has not been minutely examined.

6. Essence of Juniper boils at 320° (160° C.). It produces left-handed rotation on a ray of polarized light, and if left in contact with water gradually deposits a white crystalline hydrate (Є10H16,H2O).

14

2

(1417) 7. Oil of Caraway (Sp. gr. 0938) is obtained from the seeds of the Carum carvi; it consists of two portions; the hydrocarbon (€10H16) has been termed carvene; the oxidized portion is known as carvol. Carvene is a very fluid, colourless oil, lighter than water, with a slight agreeable odour, and an aromatic taste; it absorbs hydrochloric acid gas, and forms with it a crystallizable solid which melts at 123° (50°5 C.). Carvol, €10H1, is a liquid of sp. gr. 0953; it boils at about 437° (225° C.; Voelckel): it is isomeric with thymol and with cuminic alcohol. Carvol yields a liquid camphor (EH,HCl) with hydrochloric acid. With sulphuretted hydrogen carvol yields a compound termed hydrosulphate of carvol [(C10H14),H,S]: this substance is obtained by agitating the less volatile portion of oil of caraway with an equal bulk of alcohol recently saturated with ammonia and sulphuretted hydrogen; it is deposited in yellowish crystals, which may be recrystallized from boiling alcohol; they may be volatilized without decomposition. If this compound be agitated with an alcoholic solution of potash, it is decomposed, pure carvol is liberated and dissolved by the alcohol, and on the addition of water it rises to the surface in the form of an oily layer.

(1418) 8. Oil of Cloves (Sp. gr. 1055–1060).—The berries of the pimento and the unexpanded flower-buds of the Caryophyllus aromaticus, or cloves,' yield an essential oil which is not solidified by a cold of o° F. It consists chiefly of a hydrocarbon isomeric

588

ESSENTIAL OILS ISOMERIC WITH OIL OF TURPENTINE.

with oil of turpentine, holding in solution an acid body termed eugenic acid (E10H1202) ; sp. gr. of liquid 1'079; of vapour 6·5; boil. pt.469° (243°C.; Ettling). This acid forms a colourless liquid, which emits the odour of oil of cloves: it forms crystallizable salts with the alkali metals. Two crystallizable substances are also obtained from oil of cloves; one of them is named eugenin, and is said to be isomeric with eugenic acid. The other, termed caryophyllin, (E10H16), is isomeric with ordinary camphor; it is gradually deposited from the oil in crystalline needles.

9. Oil of Ginger (Sp. gr. 0893) is yellow, and intensely burning and aromatic. It boils at about 475° (246° C.). It appears to have the composition of a hydrate of a hydrocarbon isomeric with oil of turpentine, 8 (€10H16) 5 H2O.

(1419) 10. Oil of Cubebs (Sp. gr. 0929).—When cubebs (Piper cubeba) are distilled with water, they furnish an essence which is colourless and somewhat viscous; it has a camphreous, aromatic taste. It boils at a little below 500° (260° C.), and when distilled yields a hydrocarbon which furnishes a crystalline compound with hydrochloric acid, consisting of (Є15H24, 2 HCl). This substance fuses at 268° (131° C.). When essence of cubebs is re-distilled with water, it deposits a species of camphor (15H24, H2O), which melts at 154° (65° C.), and may be distilled at 302° (150° C.) without decomposition. The essence of cubebs, therefore, though isomeric with oil of turpentine, contains the hydrocarbon in a more condensed form, viz., as (Є1H ̧).

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11. Essence of Capivi (Sp. gr. 0·878), which is obtained by distilling balsam of capivi with water, appears to belong to the same class as that of cubebs. It boils at 500° (26c° C.), undergoing partial decomposition. It yields a crystalline compound with hydrochloric acid (EH, 2 HCI).

(1420) 12. Essence of Hops.-This essence is obtained by distilling dried hop-cones with water. The oil when first obtained is of a beautiful green colour, but it is rendered colourless by rectification. It remains liquid at 2° F., and begins to boil at about 284° (140° C.), but the boiling point rises rapidly till it exceeds 600° (316° C.). Its odour somewhat resembles that of the hop. When exposed to the air it becomes converted into an acid resinous mass. Oil of hops is a mixture of the hydrocarbon €10H16, with valerol (EH10). The hydrocarbon may be obtained in a pure form by allowing the oil to fall drop by drop upon caustic potash, when potassic carbonate and valerate are formed from the valerol:

10

13. Essence of Valerian also consists of valerol and of a hydrocarbon EH16, which is identical with borneène, the hydrocarbon which accompanies Borneo camphor (1427). By distilling off the essence at a temperature of 392° (200° C.), the borneène may be expelled. Valerol when exposed to a temperature of 32° crystallizes in transparent prisms, which do not melt until heated to 68° (20° C.). It gradually becomes oxidized by exposure to the air, and the disagreeable odour of valeric acid is developed. In its pure form its odour is but slight, resembling that of hay. Sulphuric acid dissolves it, and forms a blood-red solution, which contains a colligated sulpho-acid.

(1421) 14. Oil of Thyme.-This consists of an oxidized portion, thymol, and of a hydrocarbon, thymene. The latter constitutes the more volatile portion of the oil; it has an agreeable odour of the plant it boils at 329° (165° C.), and exerts no action on polarized light. Thymol [(1H1); Fusing pt. 111° (44° C.); Boiling pt. 446° (230° C.); Sp. gr. of vapour 5'51; Rel. wt. 75] is isomeric with carvol and with cuminic alcohol (1446); it has the agreeable odour of thyme, and constitutes about one-half of the essence of thyme. It is a fusible solid which crystallizes in oblique rhombic prisms, and is very soluble in alcohol and in ether. This substance is also contained in the oil of horse-mint (Monarda punctata), and in that of an Indian plant, the Ptychotis ajowan. Thymol combines with sulphuric acid, and forms a crystallizable colligated acid, the thymylsulphuric (HЄ10H13,SO1), which is analogous to the ethylsulphuric.

According to Lallemand, when thymol is treated with oxidizing agents such as chromic acid, or a mixture of black oxide of manganese and sulphuric acid, it yields a substance termed thymoil (€12H162),* which sublimes in brilliant orange-coloured quadrangular plates, of an aromatic odour and an appearance resembling that of quinone (1337), with which it is homologous. If treated with sulphurous anhydride or other reducing agents, it combines with hydrogen and yields thymoilol (E12H182), the homologue of hydroquinone; and by mixing a solution of equal weights of thymoil and thymoilol in boiling alcohol, the liquid immediately

It is probable that the formula of thymoil should be indicated as one half of that given by Gerhardt and Lallemand; so that thymoil should be represented as H., since it is not easy to see how a body which, like thymoil, contains in its molecule only 10 atoms of carbon, should by oxidation yield a compound containing 12 atoms of carbon.

590

ESSENTIAL OILS NOT CONTAINING OXYGEN.

becomes of a deep red colour, and deposits beautiful violet-coloure d prismatic crystals, which have a bronze lustre. These correspon d to what has been termed green hydroquinone.

(1422) Table of Essential Oils not containing Oxygen.

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(1423) Essences which contain other Hydrocarbons.-1. Oil of Peppermint. This essence, when distilled with phosphoric anhydride, yields a hydrocarbon termed menthene, €10H, The essence also appears to contain a solid hydrate of this compound (E10H18, H2O), which is analogous to camphor; this substance may be obtained in crystals; it fuses at 93° (34° C.), and boils at 416° (213°5 C.), emitting a vapour of sp. gr. 5'62.

2

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2. Essence of Cedar wood is somewhat analogous in its nature to the foregoing oil. It consists of a crystallizable solid (1H2) -dissolved in a hydrocarbon (16H26), which has been termed cedrene.

3. Attar of Roses consists also of two compounds, one of which has but little odour; it remains solid at temperatures below 203° (95° C.), and boils at about 590° (310° C.). It is polymeric with

olefiant gas.

The fragrant portion is liquid; it contains oxygen,

but its composition is not accurately known.

The table on the preceding page includes a list of the more important essences which contain unoxidized hydrocarbons.

(B.) Oxidized Essences.

(1424) Several varieties of oxidized essential oils are known; viz. :-(a) Solid crystallized essences which have the composition of hydrates of a hydrocarbon; these constitute the camphors, of which laurel camphor (E10H14, H2O) affords the best illustration. (b) Indifferent oils, such as spear-mint oil (Є10H20). (c) Aldehyds of aromatic acids, such as oil of bitter almonds (Є,H,,H), and of cinnamon (E,H,O,H). (d) Compound ethers, such as oil of winter-green (methyl salicylate, ¤H ̧‚¤‚н ̧Ð ̧).

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5

(1425) (a) CAMPHORS.-From the statements already given, it is clear that the camphors are closely related to the different varieties of turpentine. Two species of camphor are known in the east, Borneo camphor and laurel camphor; the one called Borneo camphor (E10H18) is obtained from the Dryobalanops camphora, and is so highly prized by the natives of the east that but little of it finds its way into the European market.

Laurel Camphor (E10H16, or C20H16O2); Sp. gr. of solid 0*996; of vapour 5'3147; Rel. wt. 76; Fusing pt. 347° (175° C.); Boiling pt. 399° (204° C.).—This constitutes the common camphor of the shops. The commercial supply is furnished by the Laurus camphora, but it is also produced in small quantity by many other plants, which appear to produce it by the oxidation of their essential oils. This is easily understood, since the formula of this substance is the same as that of oil of turpentine, to which I atom of oxygen has been added. The oil of lavender, of rosemary, and of marjoram, and that of several of the Labiata, such as the oil of pennyroyal and of spear-mint, contain camphor in solution. Amber, and the oils of valerian, tansy, and sage also yield it when treated with nitric acid.

Three isomeric modifications of camphor are known; they cannot be distinguished from each other, except by their action upon a ray of polarized light: one of the varieties produces rotation of the ray to the right; the second variety produces lefthanded rotation; whilst the third variety has no sensible effect upon a polarized ray. The common camphor of the shops, and that obtained by the action of nitric acid upon borneène, is the right-handed modification. The camphor contained in the oil of