These are very important raw materials for perfumes because they generally have a soft and tenacious odour. Commercial samples consist of the natural exudation from the plant together with extraneous matter which is present owing to the crude methods of collection in different parts of the world. The valuable portion of the material contains a small percentage of highly odorous essential oil and a large proportion of soluble resin. The extraneous matter is eliminated by treating the crude substance with alcohol or other solvent, filtering out the insoluble matter and concentrating the filtrate by suitable methods. Some of the more important substances coming under this head are as follows :—Benzoin is obtained from trees native to Siam, Sumatra and Java. Incisions are made in the trunk and when the bark is removed the resin flows out as a milky sap and dries in the sun. Labdanum is a secretion from the leaves of several species of a genus of the rock rose family. The modern method is to collect the leaves and extract them, as described above, by means of volatile solvents. Storax is a balsam obtained from trees occurring in vast forests in the south-west of Asia Minor. It is collected by the Yaruks who beat the outer bark of the tree in midsummer and this causes the balsam to exude into the inner bark. The outer bark is then removed and the inner bark stripped off with knives. It is boiled with water, when the balsam separates and floats to the top.
are substances of standard quality prepared by chemical means. An isolate exists in a natural prod uct and is separated from it in a nearly pure state. Examples of this are geraniol, an alcohol from palmerosa oil; carvone, a ketone from caraway oil ; eugenol, a phenol from clove oil ; safrol, a phenolic ether from camphor oil. A synthetic is "built up" from other substances, but this does not mean that it cannot exist in nature. There are many instances where a perfumery material occurs as one of the constituents of an essential oil, but it would never pay to separate it because it can be synthesised chemically much cheaper. Examples are phenyl ethyl alcohol, occurring in rose otto but synthesised from phenyl acetic esters; benzyl acetate, occurring in jasmin oil but synthesised from benzyl alcohol; linalyl acetate, occurring in lavender and bergamot oils but synthesised from acetic anhydride and linalol. Many syn thetics, however, do not, so far as is known, exist in nature but are the result of chemical research. Examples are ionone, having the odour of violets and synthesised from citral and acetone; hydroxy-citronellal, having the odour of lilies and lilac and syn thesised by hydrating citronellal ; phenyl acetic aldehyde, having the odour of hyacinths and synthesised from cinnamic acid; musk ketone, having an odour recalling that of animal musk and syn thesised by nitrating butyl-meta-xylene; d-cresyl phenylacetate, having an odour resembling that of narcissus and synthesised from coal tar liquors. Other important synthetic aromatic chemi cals are amyl salicylate—(odour of clover) ; anisic aldehyde— (odour of may-blossom) ; benzylidene acetone—(odour of sweet pea); beta naphthol ethers—(odour of orange blossom) ; cou marin—(odour of tonka-beans) ; iso-eugenol—(odour of carna tion) ; heliotropin—(odour of heliotrope) ; ethyl protocatechuic aldehyde—(odour of vanilla) ; gamma undecalactone—(odour of peaches) ; methyl phenyl acetate—(odour of gardenia) ; terpineol —(odour of lilac).
These are very widely used in the perfumery industry, not only as a basis for finished perfumes, but more particularly for scenting cosmetics. The misconception which exists concerning the crudeness of odour of these oils is altogether unfounded, especially when they have been prepared by an expert. It is quite true to say that no perfume offered to the public is entirely made from natural flower extracts. It is the absolutes skilfully blended with the synthetics, balsams and animal extracts that impart the delicious softness of odour so much appreciated. The question of price generally decides how much of the natural substance shall enter the artificial compound. For instance, a good jasmin oil made without any absolute would cost about two shillings an ounce. If about 2% of real Jasmin were added (and this proportion is necessary for the best oils) then the price would be doubled. In many cases the perfume of flowers has been analysed, not completely because so far the reactions are not known for detecting many of the mere traces of aromatics present in a flower. When a flower perfume has been analysed by present methods, however, it is a relatively simple matter to prepare an imitation from the known constituents, but there is always something lacking in the artificial odour. In order to compensate for this missing link a small quantity of the natural extract is used. In those cases where the composition of the flower perfume is not known the chemist must employ the nearest natural substance having an odour akin to that being imi tated. For instance, the composition of the perfume of violets is not known, so a small percentage of cassia absolute is used to give a natural finish to the ionone employed as its base.
These are prepared from the artificial flower oils by solution in alcohol of about 8o% strength. They ' are toned or blended with balsams, gums and oleo-resins, which retard the rate of evaporation, and small quantities of extracts of animal origin are added to give greater persistence and diffusive ness of odour. In many cases further quantities of flower extracts are added to improve the delicacy of the perfume and the whole is allowed to stand for several weeks or months in glass-lined tanks to allow it to mature. The tenacity of a scent is of the utmost importance, and the longer a perfume will remain fra grant after application to the handkerchief or garment the more popular it becomes. This is known as fixation and must be con trolled during the whole of the process of manufacture. Examples of fixators are (I) oils—patchouli, clary sage, santalwood, yeti vert ;
balsams, gums and oleo-resins—benzoin, labdanum, myrrh, oakmoss, storax; (3) synthetics—benzyl cinnamate, ethyl phthalate, coumarin, musk ambrette, heliotropin, vanillin. Many perfumes are so-called bouquets of flowery odour, yet represent ing no particular flower. In these cases the typical odour is gen erally a combination of synthetics, one of which is used in suf ficient quantity to create a new perfume note.