extent of this traffic may be imagined when it is known that in 1817 the importation of palm-oil into England did not much exceed 140,000 lbs., and that in 1836 it exceeded 70,000,000 lbs! In taking an acre of surface for unity, I find that on an average the

Aromatic plants owe the odors which characterize them to certain volatile principles, which by reason of certain properties which they have in common with fat oils, such as insolubility in water, solubility in ether and alcohol, inflammability, &c., are generally designated as essential oils. They are met with in all parts of plants; but in one plant the oil is principally found in the flower, in another in the leaves, in another in the bark, &c. It sometimes happens that different parts of the same plant contain oils of different kinds. From the orange-tree, for instance, three distinct oils are obtained, as the flower, the leaf, or the rind of the fruit is treated. In some cases the volatile principle is so thoroughly imprisoned in the vegetable cells, that drying does not dissipate it; in others, as in the greater number of flowers, the oil is formed on the surface, and is volatilized immediately after its formation.

Essential oils are less volatile than water; nevertheless they rise with the vapor of water, and it is by distillation that they are generally extracted. The plant The plant is put into a still or alembic containing water, and heat is applied the vapor formed is condensed in the receiver, and the essence, by reason of its less density, is found swimming on the surface of the water which has been distilled. Some volatile oils are obtained by pressure, those of the citron and bergamotte, for example.

The volatile principles of plants present somewhat varied physical properties. They are generally limpid and lighter than water; yet there are some which are more dense, and some, such as camphor, which are solid. With reference to their composition, volatile oils may be divided into three classes; 1st. Oils composed entirely of carbon and hydrogen. 2d. Oils composed of carbon, hydrogen, and oxygen. 3d. Essential oils containing sulphur; in addition to which, the essential oil of mustard seed contains azote.

The essential oils undergo a change by long contact with the air : they absorb oxygen, and many of them become acidified; under the influence of this gas, the oil of bitter almonds is changed into benzoic acid, the oil of cinnamon into cinn-amic acid; in a general way, acetic acid is produced. produced. The votatile oil obtained from any plant almost always contains two distinct principles, which may be separated by careful distillation; one of these principles is a carburet of hydrogen, the other an oxygenated oil. Camphor is combined with essential oils in many plants of the labiate family. It

exudes from certain laurels; it is from the Laurus camphora that all the camphor of commerce is extracted in the East, the extraction being effected precisely by the same process as other essential oils. The chips of the Laurus camphora are put into iron stills, surmounted by earthenware capitals, in the inside of which a number of ropes made of rice-straw are stretched; the camphor rises and is condensed on the surface of these cords in the state of a gray pow der; it is refined by sublimation.

According to M. Dumas, camphor contains:

Essential oils almost always hold certain substances in solution which make them viscid or sticky. The balsams which exude from the bark of certain trees are nothing more than solutions of resin in essential oils. When the volatile oil has been dissipated by evaporation, the resin remains in the solid state. There is further a natural relation in point of constitution between essential oils and resins. The greater number of essences absorb, as we have said, oxygen from the atmosphere, and by this absorption they become thick, and are changed into resins; so that in one case the resin may be a product of the oxidation of an essential oil, in another it may merely be set at liberty by the dissipation of the essence which held it in solution.

The resins constitute friable, or soft solids. They are fusible, extremely inflammable, and fixed. The resins are inodorous when pure any odor which particular resins possess is generally attributed to the essential oil which they still retain. The resins are insoluble, or very sparingly soluble in water; some of them dissolve readily in alcohol and in ether, and there are some also, such as copal, which are only soluble in very small quantity. Some resins show acid reaction; they combine with bases, neutralizing them. The greater number of resinous matters obtained from plants are regarded by chemists as mixtures of several particular resins, the study of which is not yet much advanced. Some resins are much employed in the arts, such as colophony and copal, &c. Several balsams are also in familiar use, particularly as medicines, such as the balsam of tolu, balsam of copaiba, &c.

Colophony, or rosin, is extracted from different kinds of the genus Pinus. In the Landes, or sandy plains of Bordeaux, it is the maritime pine which yields it. When the tree is from thirty to forty years of age, incisions are made in the trunk, beginning at the lower part, two or three times a week, and these are continued to the height of from 6 to 10 feet from the ground; the last notch generally reaches this height about four years after the tree has been notched for the first time. After this a new series of notches is begun on the opposite side, setting out from the ground as before, and in

this way the whole circumference of the tree finally presents a series of notches, so that a tree will continue to yield turpentine during a period of sixty years. The turpentine which exudes from the notches is collected in a hole dug in the ground.

Crude turpentine always contains a quantity of intermixed foreign matters, earth, stones, leaves, &c. It is purified by being melted, and filtered hot through a bed of straw. By distillation it is separated into essential oil, which is condensed in the receiver, and colophony, or rosin, which remains in the still. From 250 lbs. of turpentine 30 lbs. of essence and 220 lbs. of rosin are generally obtained.

Copal is the produce of a tree which is somewhat common in Madagascar, and which M. Perrotet has determined to be the Hymenaa verrucosa. The balsam or sap which exudes from the bark solidifies by contact with the air, and the resin is gathered in the state in which it is met with in commerce.

CAOUTCHOUC.

The caoutchouc which we have mentioned as forming a constituent in the sap of certain trees possesses some properties which assimilate it with the resins. Thus pure ether, free from alcohol, dissolves it. The greater number of the essential oils also dissolve it, particularly when hot. It is a solution of Indian rubber in rectified coal-tar oil or naphtha, which is now used so extensively for making stuffs water-proof. According to Faraday pure caoutchouc is composed of:

Some plants produce a considerable quantity of a substance which bears a great resemblance to beeswax, and which in some of its properties approaches fatty bodies. Proust discovered that vegetable wax formed part of the green fecula of a great number of vegetables. In the common cabbage it occurs in large quantity. It is often met with forming a varnish on the surface of leaves, fruit, and barks; the substance, however, is far from being identical; it almost always results from the combination of several distinct principles which have not yet been sufficiently studied, but among which there are obviously some true fatty substances, that is to say, bodies capable of saponification, and matters analogous to the resins. I shall here mention a few of the vegetable waxes which are best known.

Wax of the palm. This is the product of the Ceroxylon andicola, which is very abundant on the central Cordillera of New Grenada. I believe that I met with the lower limit of the ceroxylon upon the borders of the torrent of Tochecito, at the height of 7500 feet above the level of the sea, and I followed it to an absolute elevation of about 8500 feet. The extreme mean temperatures comprised be

tween these two limits may be valued at from 11° to 18° cent. ; 51.8° to 64.4° Fahr. Towards the superior limit, the ceroxylon is exposed to a cold during the night, which approaches the freezing point of water; it is therefore frequently met with in company with the great oak of America, whose climate it stands very well.

The Indians obtain the wax by scraping the bark of the palm: the scrapings are then boiled in water; the wax swims-without, however, melting; it is merely softened, and the impurities which it contains are deposited. The matter thus purified is formed into balls and set to dry in the sun. It is with this substance, to which,

however, a small quantity of fat is often added to render it less brittle, that the loaves of wax and the candles of the country are formed. After it has been melted, the cera de palma is of a deep yellow color, slightly translucid, as brittle as resin, and presenting a waxy fracture well characterized. Its melting point is a little above that of boiling water. Boiling alcohol dissolves it readily; in cooling, the solution sets into a gelatinous mass. Ether dissolves it, as do the alkalies also.

The wax of the palm consists of two principles; one, fusible above the temperature of the boiling point of water, has all the physical properties of beeswax; the other has the properties of resin. The composition of these substances upon analysis appears to be:

Wax.

Resin.

Wax of the Myrica cerifera. This wax is procured by boiling The tree is exthe fruit of several species of myrica in water. tremely common in Louisiana and the temperate regions of the Andes. The fruit yields as much as 25 per cent. of wax, and a single shrub will yield from 24 to 30 lbs. of berries per annum. The crude wax is green, brittle, and, to be made into candles, requires the addition of a certain quantity of grease. According to M. Chevreul the wax of the myrica is saponifiable.

Wax of the sugar-cane. The sugar-cane, particularly the violet variety, is covered with a powder or bloom of a waxy nature, which melts at the temperature of 82° cent. (180° Fahr.) This wax is so hard that it can be pulverized; it may be made into candles, which, for the brilliancy of their light, are not inferior to those of spermaceti. M. Avequin, who directed attention to this subject, found by his experiments that a hectare (nearly 2 acres English) of the This wax is violet cane would furnish nearly 200 lbs. of wax. entirely soluble in boiling alcohol; ether does not dissolve it in the cold. It appears to constitute a perfectly defined immediate vegetable principle, the composition of which, according to M. Dumas, is the following:

Carbon
Hydrogen
Oxygen

81.4

14.1

4.5

100

CHLOROPHYLLE.

The green matter which colors the leaves of vegetables is so designated. The attempts which have been made to isolate this matter, render it probable that it is somewhat of the nature of the vegetable waxes. Pelletier and Caventou endeavored to procure it by treating with cold alcohol, the pulp remaining after expressing all the juices from the leaves of various herbaceous plants. By evaporation of the alcoholic liquor, a substance of a deep-green color was obtained, which is chlorophylle, a matter soluble in ether, in alcohol, the oils, and the alkalies. Heated, it softens and is decomposed before it melts. Acetic acid dissolves it in very appreciable quantities, so do the sulphuric and hydrochloric acids; water precipitates it from these acid solutions. Berzelius says that chlorophylle exists only in very small quantity in plants, the leaves of a large tree will not perhaps contain more than about 100 grains.

OF COLORING MATTERS.

The matters which color the different parts of plants are extremely numerous; they present great varieties of shade, but are in general derived from red, yellow, and green. It is seldom that the coloring matter of a plant exists isolatedly; it is almost always allied with one or several immediate principles, which are themselves frequently colored. Thus red coloring matters are generally combined with yellow principles, which having nearly the same properties, one is with great difficulty separated from another.

Coloring matters are solid, inodorous, and have little taste. Some are soluble in water, others only dissolve in alcohol or in ether. All combine with the alkalies, and several of them unite intimately with acids; the greater number are powerfully affected, undergo a true destruction, on exposure to the sun's rays, especially when in contact with moist air. It is familiarly known that vegetable tissues of all kinds, beeswax, &c., are bleached by exposure to the sun and air; a high temperature acts like light: some vegetable colors aie altered, bleached, when they remain exposed for a time to a temperature of from 334° to 424° Fahr. The oxygen of the air, which so quickly destroys certain colors, develops others under particular circumstances.

Alkalies and acids, by uniting with vegetable colors, almost always modify their tints and often change them entirely. Many blues, for instance, become reds, under the agency of acids, greens or yellows under that of alkalies. By neutralizing the acid or the alkali, the color generally resumes its original tint.

Several substances, which are colorless in the state in which they are formed in vegetables, become colored by the united action of oxygen and an alkali, such as orceine, which is oxidated and becomes blue under the simultaneous contact of air and ammonia. The greater number of vegetable coloring matters are destroyed