ODOURS DEFINITE AND FIXED. 183 Cologne-called the perfection of perfumery-depends for its excellency on the same principle." * Odours resemble very much the notes of a musical instrument. Some of them blend easily and naturally with each other, producing a harmonious impression, as it were, on the sense of smell. Heliotrope, vanilla, orange blossoms, and the almond blend together in this way, and produce different degrees of a nearly similar effect. The same is the case with citron, lemon, vervain, and orange peel, only these produce a stronger impression, or belong, so to speak, to a higher octave of smells. And again, patchouly, sandalwood, and vitivert form a third class. It requires, of course, a nice or well-trained sense of smell to perceive this harmony of odours, and to detect the presence of a discordant note. But it is by the skilful admixture, in kind and quantity, of odours producing a similar impression, that the most delicate and unchangeable fragrances are manufactured. When perfumes which strike the same key of the olfactory nerve are mixed together for handkerchief use, no idea of a different scent is awakened as the odour dies away; but when they are not mixed upon this principle perfumes are often spoken of as becoming sickly or faint, after they have been a short time in use. A change of odour of this kind is never perceived in genuine eau de Cologne. Oils of lemons, juniper, and rosemary are among those which are mixed and blended together in this perfume. None of them, however, can be separately distinguished by the ordinary sense of smell; but if a few drops of hartshorn be added to an ounce measure of the water, the lemon smell usually becomes very distinct. But though, as I have said, each volatile essence is chemically distinct, and possesses properties peculiar to itself, * Report of the Juries of the Great Exhibition of 1851, p. 608. among which the odour is one, yet the delicacy and fragrance of this odour is found to vary considerably with the locality in which the plant that yields it has been grown. Thus on the shores of the Mediterranean, near Grasse and Nice, the orange tree and the mignonette bloom to perfection in the low, warm and sheltered spots: while, in the same region, the violet grows sweeter as we ascend from the lowest land and approach to the foot of the Alps. So lavender and peppermint grown at Mitcham, in Surrey, yield oils which far excel those of France or other foreign countries, and which bring eight times the price in the market. This effect of soil and climate on the odour of plants resembles that which they exercise in so remarkable a manner on the narcotic constituents of tobacco, opium, and hemp.* The small proportion of volatile oil which many flowers yield by distillation has led to other modes of extracting it for use in perfumery. The flowers are moistened with olive or other oil, or with pomatum, and, after lying for a while, are submitted to pressure; or they are put into hot water and well shaken, with a portion of oil or pomatum, which is afterwards skimmed off. In either way the oil or fat is impregnated more or less strongly with the odour of the flowers, and has acquired a proportionate value. This process is called maceration, enfleurage, &c., and fats so perfumed are generally called French pomatums. Spirit of wine extracts the odoriferous principle from these scented fats, and the solutions are employed for the manufacture of perfumed waters. The economical importance of these essential oils may be judged of from the facts that, In 1852 there were imported into this country of essential oils about 200,000 lb. weight, paying a duty of is. a-pound; Eau de Cologne to the value of £20,000 sterling; * See THE NARCOTICS WE INDULGE IN. COMPOSITION OF THESE OILS. French pomatums and other perfumery valued at £2200; 185 And that the total duty of every kind paid in Great Britain, for scents and perfumes, has been calculated at £40,000 a-year.* 2o. COMPOSITIONS OF THE VOLATILE OILS.-A large number of the odoriferous essences of plants is composed of the two elementary bodies, carbon and hydrogen only. And what is very remarkable, many of them, which are otherwise very distinct, consist of these two elements united together in the same proportions. Thus a hundred pounds of pure oil of turpentine consist of — And the oils of lemons, of oranges, of juniper, of rosemary, of copaiba, of the queen of the meadow, and many others, though so different in their properties from the oil of turpentine and from each other, consist of exactly the same proportion (881⁄2 lb.) of carbon united to the same weight (113 lb.) of hydrogen. Substances thus differing in properties, and yet agreeing in composition, are distinguished among chemists * The quantities of essential oils paying 1s. a-pound duty entered for home consumption in 1853 were as follows: The otto of roses comes chiefly from Constantinople and Smyrna; the oil of lemons from Sicily and Portugal; bergamot in large proportion from Sicily; and anise from Germany and the East Indies. The oil of cloves imported is small in quantity; but the consumption is probably ten times as much, the English wholesale druggists being themselves large distillers of this oil. Carraway is also largely distilled at home, while of oil of lavender probably as much as 6000 lb. are distilled in England, besides much oil of peppermint. by the name of Isomeric bodies. The difference of proper ties they exhibit is believed to be a consequence of the unlike ways in which the minute molecules or atoms of the carbon and hydrogen are arranged and grouped together in the different compounds. Another class of these volatile odoriferous oils contains a small proportion of oxygen combined with the carbon and hydrogen of which they chiefly consist. To this class belongs the volatile oil which bitter almonds (fig. 77) yield when distilled with water. This fragrant oil is very different from the fixed oil which almonds, both sweet and bitter, yield when submitted to pressure, and is much used by the confectioner and cook. Fig. 77. Fig. 78. Amygdalus communis, var. amara- Scale, 1 inch to 20 feet. Scale for flowers, leaf, fruit, stone, and kernel, 1 inch to 3 inches. Cinnamonium zeylanicum-Tho Scale, 1 inch to 20 feet. Of the same kind is the oil of cinnamon, which the young bark of the cinnamon laurel (fig. 78) yields when distilled with water; and also the oil which is obtained from anise seed by a similar process. But in this class, the proportions ARTIFICIAL ESSENCES. 187 of the several constituents are rarely the same in two different oils. Thus the three oils above mentioned consist Oil of peppermint and many others belong to this class. They all differ from one another in composition, the proportions of the three ingredients varying in each case. 3o. ARTIFICIAL ESSENCES.-It is a character of all the volatile oils of the kinds above mentioned, that they cannot as yet be formed or imitated by chemical art. The progress of chemistry, however, has recently made us acquainted with one odoriferous essence, somewhat peculiar in kind, which can be prepared by an artificial process; and this is probably only the forerunner of many similar discoveries by which our power over matter is hereafter to be enlarged. I have already mentioned the volatile oil of the queen of the meadow (Spirea ulmaria), fig. 79, as having the same composition as oil of turpentine. But when the flowers of this plant are distilled with water, they yield, besides this oil, another sweet-smelling substance, known as the essence of spiræa, which differs from the oil in its properties, has a different composition, and contains oxygen. This essence resem. bles in its odour the oil of bitter almonds, and is remarkable for possessing acid properties. Fig. 79. Spiræa ulmaria-The Queen |