PERFUMES, substances, generally of complex composition, which by reason of their fragrance gratify the sense of smell. The history of perfumes is closely associated with that of cosmetics (q.v.), and many of the earliest forms were made by digesting odorous vegetable substances with sesame, almond or olive oil. The principle underlying this process is still made use of although in an improved form and will be referred to later under Macera tion.
These are the product of plant metabol ism and their highest form is found in the scent of fresh flowers. This fragrance is due to the occurrence in the petals of minute traces of essential oil which in rose and lavendar is in the free state, whereas in jasmin and tuberose it is in the form of a glucoside. Under favourable conditions this complex substance is progressively decomposed in the presence of an enzyme or ferment with the formation of a volatile oil. The occurrence of natural perfume is, however, by no means confined to the inflo rescence but frequently exists in other parts of the vegetable organism. Briefly it is found in the flowers of cassia, carnation, clove, hyacinth, heliotrope, mimosa, jpsmin, jonquille, orange blossom, rose, reseda, violet and ylang ylang; flowers and leaves of lavender, rosemary, peppermint and violet ; leaves and stems of geranium, cinnamon and patchouli; barks of cinnamon and cassia; woods of cedar, linaloe and santal; roots of angelica, sassafras and vetivert ; rhizomes of calamus, ginger and orris; fruits of bergamot, lemon, lime and orange ; seeds of bitter almonds, anise and nutmeg; gums or oleo-resinous exudations from myrrh, peru balsam, storax and tolu.
As mentioned above, the odoriferous constituents of the plant generally occur as a volatile oil which, after separation as de scribed below, is a highly aromatic, mobile liquid. This usually contains several individual bodies, differing chemically, and to one or more of these the typical odour of the oil is due. Chemistry has been able in many cases to establish definitely these princi pal constituents, as, for instance, the odour of almond oil is attributed principally to benzaldehyde, of clove oil to eugenol and of lemon oil to citral. Where the oil is of complex composition, the typical odour is believed to be due to several perfectly blended constituents. For instance, in rose otto the higher aliphatic alde hydes in minute traces, together with the esters of the alcohols geraniol and citronellol, undoubtedly determine the distinctive rose fragrance. The separation of these natural odoriferous ma
terials from the plant is no easy matter since a process that is suitable for one is of no use for another because the delicate perfume substance may be destroyed or decomposed or, further more, may be incompletely extracted. It will be best to describe briefly each process of the plant material under treatment.
This is effected by either boiling the vegetable organism with water in a closed apparatus when the source of heat may be an open fire or a steam-heated coil or jacket in the bottom; or by blowing live steam through the material. In each case the still is connected at the top with a condenser, through which the steam passes, carrying with it in suspension the fine particles of essential oil, the condensed steam and oil emerging from the lower orifice. On standing aside the oil floats to the top and is separated. Distillation with . an open fire is the oldest process and in places far distant from modern factories this is resorted to by the peasants. It is, however, not free from dan ger, for if the water in the apparatus gets low the material is burnt, then the odour of the resulting oil is impaired. In some parts of Bulgaria this method is used for preparing rose otto and in some parts of India for distilling palmerosa oil. When steam is used for distillation a separate boiler is erected near by and the question of damaging the oil by burning is therefore eliminated. Generally the raw material does not touch the bottom of the apparatus but is supported upon a false bottom or perforated sheet of metal and sometimes placed in an open wire basket suspended inside. In some cases the water used for distillation dissolves part of the oil or its constituents. It is sold separately, as, for instance, rose water or orange-flower water. Modern apparatus as used in Europe and America is often required to take one ton of material, such as lavender or peppermint, the capacity of the still being about 1,200 gallons. This process is applicable to the majority of the vegetable organisms mentioned above, the principal exceptions being some of the flowers and most of the fruits.