what we usually call the necessaries of life, that we naturally hesitate to believe what we are so unable to explain. The more we consider, however, the statements contained in this and the preceding chapters regarding the beverages, the narcotics, and the poisons, the more we shall be satisfied of the imperfect state of our knowledge as to what concerns the maintenance and comfort of our lives. We are especially ignorant still of the conditions as to quantity and forms of food under which man will refuse to live in the varied circumstances of climate, habit, and constitution to which he is subject. But this will come under our notice again, in a succeeding chapter, when we consider WHAT, HOW, AND WHY

WE DIGEST.

CHAPTER XXIV.

THE ODOURS WE ENJOY.

VOLATILE OILS AND FRAGRANT RESINS.

Vegetable odours.—The volatile oils; how extracted.—Quantity yielded by plantaThe otto of roses; how collected. The oils exist in different parts of plants.Simple and mixed perfumes.-Analogy between odours and sweet sounds.Odours may resemble and blend with each other.-Extraction of oils by maceration.-Quantity of volatile oils imported.-Composition of oils of lemons, oranges, &c.-Isomeric oils.-Oils containing oxygen.-Volatile oils of almonds and cinnamon.-Artificial essences.-Oil of spiraa; can be prepared by art.-Manufactured substitutes for oil of bitter almonds.-Nitro-benzol, or essence de Mirbane.-Nitrobenzyl another substitute.-The camphors.-Chinese and Borneo camphors.-Balsams of Peru and Tolu.-The odoriferous resins; why they become fragrant on red-hot charcoal; their use as incense.-Vanilla, its fragrance, and analogy to the balsams.-The Tonka bean; coumarin, the odoriferous principle of this bean.The same principle in vernal grass, melilot, and other plants.-Gives fragrance to hay, and probably produces hay fever.

AMONG the appliances of common life by which the comfort of man in a civilized state is very materially affected, are the odours he enjoys and the smells he dislikes. Upon the ori gin, nature, mutual relations, and physiological action of these, modern chemistry has thrown much light. I shall, therefore, in this place briefly illustrate their chemical history.

The odours we enjoy are nearly all derived, either directly or indirectly, from the vegetable kingdom. Among scents in common use, musk, civet, and ambergris, are the only ones which owe their origin to animal life; while with pleasant smells of a purely mineral origin we are as yet altogether unacquainted.

I. VEGETABLE ODOURS.-The odoriferous substances yielded by plants are of three kinds-the volatile oils, such as the oils of lemons and lavender-the camphors, balsams, and sweet-smelling resins-and the volatile ethers, such as those which give their agreeable bouquet to different kinds of wine.

10. THE VOLATILE OILS.- When the parts of odoriferous plants are distilled with water, an oil passes over along with the steam, and floats on the surface of the water, which condenses in the receiver. This volatile oil usually exhibits in a high degree the peculiar smell, and often also the taste of the plant from which it is extracted. In this way are obtained the oils of roses, lavender, lemons, oranges, orange flowers, cinnamon, peppermint, and many others, which in smell and taste remind us at once of the plants from which they have been distilled.

the surface But this wasolution, and

Thus rose

The greater part of the oil usually floats on of the water which distils over along with it. ter always retains a small portion of the oil in from this oil it acquires both smell and taste. water, lavender-water, peppermint-water, &c., are simply waters impregnated with a minute quantity of the oil from which they severally derive their names. The water distilled from myrtle flowers forms that very agreeable perfume known in France by the name of eau d'ange.

The quantity of oil yielded by some plants is so small, that the water which distils over along with it retains it all in

solution. In such cases the oil is difficult to obtain, and is in consequence very expensive. Roses are among the flowers which yield their oil in such minute quantities, and hence the high price of the pure attar of roses. The rose-gardens at Ghazepore are fields in which small rose-bushes are planted in rows. In the morning they are red with blossoms, but these are all gathered before mid-day, and their leaves distilled in clay stills, with twice their weight of water. The water which comes over is placed in open vessels, covered with a moist muslin cloth to keep out dust and flies, and exposed all night to the cool air or to artificial cold-as we set out milk to throw up its cream. In the morning, a thin film of oil has collected on the top, which is swept off with a feather, and carefully transferred to a small phial. This is repeated, night after night, till nearly the whole of the oil is separated from the water. Twenty thousand roses are required to yield a rupee weight of oil, which sells for £10 sterling(HOOKER).* Pure attar of roses is therefore rarely to be met with. That which is sold in the Indian bazaars is adulterated with sandal-wood oil, or diluted with sweet salad oils. What we obtain in Europe is generally still more diluted, as the price we usually give for it sufficiently shows.

The odoriferous principle is not always diffused uniformly over the whole plant. In some, as in mint and thyme, it resides in the leaves and stem; in others, as in the cinnamon tree, it is in the bark; in others, as in the sandal and cedar trees, it is in the wood; in others, like the rose, the lily, the violet, and the jasmin,† it is in the leaves of the flower. In many, like the Tonquin bean, the anise, and the

*The weight of a rupee is something less than 176 grains. Others say that a thousand roses yield less than two grains of oil. Of course the quantity must vary very much as the scent of the rose is greater or less.

+ Pure il of jasmin is almost as rare and dear as pure attar of roses. At the Great Exhibition of 1851, six ounces of it were exhibited, the price of which was nine pounds

an ounce.

carraway, it is in the seed; while in some, like ginger, the iris, and the vitivert, it is in the root. It sometimes even happens that distinctly different scents are extracted from different parts of the same plant. Thus the orange tree, from its leaves, yields a perfume called petit grain-from its flowers, another called neroli-and from the rind of its fruit the essential oil of oranges, called also essence of Portugal.

These volatile oils and scented waters are used as perfumes for the toilet, to flavour the bonbons of the confectioner, or for giving an agreeable relish to the finer dishes of the cook. The oils of roses, lavender, orange flowers, &c., are sold only for toilet use, and for scenting the preparations of the perfumer; while those of lemons, peppermint, cinnamon, cloves, ginger, &c., are employed almost solely by the confectioner and the cook.

Every pure volatile oil is a definite chemical compound, possessed of properties which are constant and peculiar to itself. Among other properties, it possesses an odour, more or less pronounced, by which it can in most cases readily be recognised. Upon this odour, when agreeable, its value and estimation depend; and the quality of the odour determines the purpose, in perfumery or otherwise, for which it is em ployed. The pure and unmixed odours of such single oils are often highly esteemed, and by some persons preferred to all other scents. But in preparing delicate perfumes it is seldom that a single oil, or the parts of one plant only, are employed for the purpose. The art of the perfumer is shown by the skill with which he combines together the odoriferous principles of various flowers, or mingles together many volatile essences, so as to produce a more grateful scent than any single plant can be made to yield. In this way the huille de mille fleurs (oil of a thousand flowers) professes to be made; and the secret recipe for the popular Eau de