THE PERFUME-MATERIALS FOR THE MANUFACTURE OF PERFUMERY.

Most of the perfume-materials employed by the perfumer are derived from the vegetable kingdom; a few are of animal origin, whilst some are artificially prepared.

Of animal substances only four are used, namely: musk, castor or castoreum, civet, and ambergris; the separation of their characteristic odoriferous substances has, however, not yet been accomplished. The odor of plants is generally due to volatile substances called volatile or essential oils. Their occurrence is not limited to special parts, they being found in the flower, seed, wood, bast, bark, leaves, and root. However, in every plant the oil occurs chiefly in certain organs, and it even happens that the oil differs with the part of the plant whence it is derived. The odors exist already formed in the living plant, or else are generated, as in the instance of bitter almonds, by some reaction between the elements which takes place during fermentation or distillation.

From the strength of the odor of a plant no conclusion can be drawn as to the quantity of volatile oil present. If this were the case, the hyacinth, for instance, would contain more oil than the coniferae, whilst in fact it contains so little that it can be separated only with the greatest difficulty. The odor does not depend on the quantity, but on the quality of the oil; a plant may diffuse but little odor and still contain much volatile oil. Of the various families of plants, the labiatae, umbelliferae, and coniferae are richest in volatile oils.

In every climate plants diffuse odor, those growing in tropical latitudes being more prolific in this respect than the plants of colder regions, which, however, yield the most delicate perfume. Although the East Indies, Ceylon, Peru, and Mexico afford some of the choicest perfumes, Central Europe is the actual flower garden of the perfumer, Grasse, Cannes, and Nice being the principal places for the production of perfume-materials. Thanks to the geographical position of these places, the cultivator, within a comparatively narrow space, has at his disposal various climates suitable for the most perfect development of the plants. The Acacia Farnesiana grows on the seashore, without having to fear frost, which in one night might destroy the entire crop, while at the foot of the Alps, on Mount Esteral, the violet diffuses a much sweeter odor than in the hotter regions, where the olive and the tuberose reach perfect bloom. England asserts its superiority in oils of lavender and peppermint. The volatile oils obtained from plants cultivated in Mitcham and Hitchin command a considerably higher price than those from other localities, this preference being justified only by the delicacy of their perfume. Cannes is best suited for roses, acacias, jasmine, and neroli, while in Nimes, thyme, rosemary, and lavender are chiefly cultivated. Nice is celebrated for its violets, while Sicily furnishes the lemon and orange, and Italy the iris and bergamotte.

The odors exhaled by our own domestic plants have been but little studied, but the southern as well as many northern districts of the United States are well adapted for the cultivation of quite a number of species of plants which might be made to yield highly valuable articles of commerce. Among the plants which might furnish oils for the perfumer's use are, for instance, the wall flower, the Lilly, lilac and mignonette.

Volatile Oils.—The volatile oils are either fluid (actual volatile oils) or solid (varieties of camphor) or solutions of solid combinations in fluid. The latter, on exposure to low temperatures, separate into two portions, one solid, called stearoptene, and the other liquid, called elÆoptene. The boiling point of the volatile oils is considerably higher than that of water, but when heated with water they pass over with the vapors. Upon paper, fluid volatile oils produce grease spots, which differ, however, from those caused by fat oils in that they gradually disappear at an ordinary temperature, and rapidly by gentle heating. Most volatile oils are insoluble, or only with difficulty and sparingly soluble, in water, but they impart to the latter their odor and taste. They are readily soluble in alcohol, ether, chloroform, bisulphide of carbon and petroleum-ether, and miscible in every proportion with fats and fat oils. By their solubility in alcohol they differ from most fat oils. When freshly prepared many volatile oils are colorless, but soon turn yellow; some, however, show a distinct color even when fresh. They ignite with greater ease than fat oils and burn with a fierce smoky flame depositing a large amount of carbon. They exhibit a great tendency to absorb oxygen from the air and to gum, the influence of light promoting the process. In specific gravity they range from about 0.75 to 1.17, most of them being specifically lighter than water. Most bodies, under otherwise equal conditions, show always exactly the same specific gravity, the variations being so slight that they may be justly ascribed to errors of observation. However, one and the same volatile oil frequently shows such variations in specific gravity, that we are forced to ascribe this phenomenon to alterations in the constitution of the oil itself. For the exact determination of the specific gravity of a volatile oil, it should, therefore, be subjected to examination immediately after its preparation from the plant or vegetable substance, which should be as fresh as possible. The influence of light upon volatile oils is best shown by the following interesting experiment: If certain volatile oils are distilled in a vacuum or over burnt lime in a current of carbonic acid, it is no longer possible to distinguish, for instance, oil of lemon from oil of turpentine; however, by again exposing the oils to the air, they reacquire their characteristic odor.

According to their elementary composition the volatile oils may be divided into three principal divisions:—

1. Volatile oils free from oxygen, terpene (camphene), or hydrocarbons.

2. Oxygenated volatile oils.

3. Volatile oils containing sulphur.

On account of the facility with which most of the volatile oils absorb oxygen, oils originally free from oxygen are frequently a mixture of hydrocarbons and combinations containing oxygen. The volatile oils varying so much in their physical as well as their chemical properties, a suitable classification of them has thus far been unsuccessful.

Most of the volatile oils contain a liquid hydrocarbon, terpene, which is characterized neither by special taste nor odor, nor is the peculiarity of a volatile oil dependent on it. In the direct distillation of a volatile oil, for instance, lemon oil, this hydrocarbon (citrene), passes first over and can, therefore, be readily separated from the constituents on which depend the peculiarity of lemon oil, and which distil over at a higher temperature. The specific character of an oil is generally due to the portion of the oil containing oxygen. Hence, manufacturers have endeavored to free several of the volatile oils, used for perfumery and the preparation of food, from the worthless terpene and at the same time to obtain them in a concentrated form. Carvol is, for instance, caraway oil freed from carvene (terpene). These concentrated oils are not only purer and more agreeable in odor and taste and more readily soluble in dilute alcohol, but, being more concentrated, an equal volume of them goes much further than ordinary volatile oil. In the price lists these oils are designated as extra strong, patented, concentrated, highly concentrated oils or essences.

All the terpenes occurring in the various oils are combinations having the formula C₁₀H₁₆, or polymeric with it, C₁₅H₂₄, C₂₀H₃₂, etc. These terpenes exhibiting certain deviations in regard to their properties, odor, specific gravity, and boiling points, nearly as many terpenes as there are volatile oils have been distinguished. It is, however, very likely that these deviations may be traced back to fortuitous circumstances, for example, to the admixture of foreign substances occurring together with the terpenes, and that, by a more accurate examination, the number of terpenes entitled to be considered pure chemical combinations will be considerably reduced. By Wallach's labors, the identity of several terpenes formerly considered distinct, has already been established, whilst many others have been found to possess properties in common.

According to the nature and quantity of the odoriferous substances contained in the plants, various methods, namely, expression, distillation, extraction, maceration, and absorption, are employed for the purpose of obtaining them.

Expression.—This is only practicable when the substances are especially rich in oil and of sufficient softness, as in the case with the peel of the orange, citron, lemon, etc. In such instances the material is simply placed in a linen cloth and subjected to a strong pressure until it ceases to yield oil. The press may be of any size according to the quantity to be expressed. For small quantities it generally consists of an iron vessel, having a small opening at the bottom so that the oil may flow out. The material is placed upon a perforated bottom inside of the vessel and covered with a well-fitting iron plate, that can be pressed down by means of a screw. Though the material is fairly exhausted by such a press, for large operations it is advisable to make use of a hydraulic press, which is constructed and managed in exactly the same manner as those used for the expression of fixed oils.

By expression a turbid milky fluid is obtained, which consists of the volatile oil and aqueous substances. The latter are a solution of various extractive substances and salts in water. This fluid, as it runs from the press, is received in tall, narrow, glass vessels and brought into a cool place for clarification. This frequently requires several days, three distinct layers being generally distinguished. On the bottom is a mucous layer consisting of cell substances carried along by the liquid bodies. Over this is a clear fluid consisting of a solution of extractive substances, vegetable albumen, and salts, and upon this floats the volatile oil, being specifically the lightest body, which, by its greater refractive power, can be clearly distinguished from the aqueous fluid.

The oil is separated by bringing all that has been expressed into a bottle provided near the bottom with a lateral neck closed by a cock. After separating the oil from the aqueous fluid, the latter is allowed to escape by opening the cock.

The oil obtained in this manner is still impure, and requires further treatment to remove small vegetable fibres, invisible to the naked eye, which float in them, and cause them to be somewhat opaque and slightly opalescent. By their subsequent decomposition they would also give the oil a disagreeable odor.

There are two methods of obtaining the oil entirely clear, viz., filtration and distillation. Filtration is the cheaper process, but requires special precautions to exclude the air as much as possible to prevent the oil from undergoing injurious changes. By arranging the filtering apparatus so that the oil always comes in contact with only the same quantity of air, the injurious action of the oxygen is reduced to a minimum. It is self-evident that the apparatus should not be placed in the sun, but in a semi-dark, cool place.

A filter of simple construction, and performing excellent service, is shown in Fig. 1. It consists of a large glass bottle, F, hermetically closed by a doubly-perforated cork. The neck of the glass funnel T, the upper rim of which is ground smooth, is placed in one of the holes, and a glass tube, r, bent at a right angle, is fitted into the second hole. A thick wooden lid, with a rubber ring on the lower side, is placed upon the funnel, thus closing it air-tight. In the centre of the lid is fitted a glass tube, r´, also bent at a right angle, which is connected with the tube r, by a rubber hose, k. After the funnel has been provided with filtering paper and the oil to be filtered, the lid is placed upon it, and must not be removed, except for the purpose of pouring more oil into the funnel. The air in the bottle F is displaced by the oil dropping into it, and escapes through r, k and r´ into the funnel, and thus only the air in the bottle and funnel can act upon the oil.

The other method for the complete purification of expressed oil is by rectification or distillation with water. For this purpose the oil, together with a little water, is brought into one of the stills described later on, and the oil distilled over. It is sometimes difficult to obtain the last portion of the oil, especially with a still heated by direct fire, and it is therefore preferable to combine it with a fresh quantity of the same oil to be distilled.

Distillation.—There are at present two methods in use. The one is founded upon the direct action of the heat, the other upon the use of steam. The first was formerly in general practice, and is still largely employed in France and England, and to a limited extent in this country. It is, however, very deficient in many respects. As the stills must necessarily be of small capacity, only small quantities can be distilled at one time, and the oils very rarely possess the peculiar odor due to them, and sometimes the odor is even altered. In mixing too little water with the materials to be extracted, there is danger that empyreumatic oils will be formed; a large quantity of water, on the other hand, is of disadvantage, in so far as in case the perfume-materials contain little oil, only a perfumed water, but no oil, will be obtained. In order to avoid these inconveniences, or, at least, to do away with some of them, another plan was devised. The materials to be distilled were spread upon sieves, which were suspended in the upper part of a still, so that they might be penetrated from below. It is true no scorching is possible in this case, as was in the other process when the heating was continued after all the water had evaporated, and the oil retains its proper color, but by this method only small quantities can be extracted at a time. The still generally used for distillation with direct heat resembles so much an ordinary whiskey still as to need no further description here.

For the accurate determination of the percentage of volatile oil a vegetable substance will yield, or to obtain the oil from very costly raw materials, the small glass apparatus, Fig. 2, is used. The flask A, with a capacity of up to 5 or 6 quarts, serves for a still. In the tube t, shaped like the neck of a bottle, is inserted by means of a cork, a funnel tube, l, reaching to the bottom of the flask. The neck of the flask passes into the cooling pipe, which lies in a so-called Liebig cooler. This consists of a wide-glass tube, C, into the lower end of which, at h, flows cold water from the reservoir D, displacing the heated water at g. The lower end of the cooling pipe is connected with the neck-shaped tube v, under which stands the vessel for the reception of the distillate. To prevent the cracking of the flask, which might readily happen with the use of direct heat, it is placed in a vessel filled with sand or water.

A very good small apparatus for the distillation of volatile oil is shown in Fig. 3. It is known as a siphon still. It consists of a double-walled boiler, surmounted by a still-head, which is provided with a mechanism for keeping the contents of the boiler in motion. This stirring apparatus consists of a perpendicular shaft, bearing a frame work of iron, curved so as to correspond to the interior shape of the still, and on the outside carrying a chain which scrapes over the inner surface of the still while the stirrer is being turned. This may be done either by hand or by steam. The still having been charged with the material to be extracted, is filled up with water to within a few inches of the top of the body of the still, and the latter is heated by admitting steam. The vapors arising are conducted to a cooler situated at a higher level than the still itself, and the condensed liquid is collected in a receiver, where the oil and water separate. This receiver is provided with two faucets, one near the top and the other near the bottom. If the oil passing over is heavier than water, the excess of the latter is removed by the upper faucet; if the oil swims on the water, the lower faucet is regulated so as to allow the water to escape in about the same ratio as it enters the receiver. In either case the condensed water is made to run back into the still, and the loss of oil is, therefore, greatly reduced.

Sometimes a single-walled still is used, and distillation carried on with direct steam. This method is, however, not suitable where the presence of water is necessary, for instance, in the production of oil of bitter almonds.

A simple way of converting an ordinary still into use with steam is shown in Fig. 4. For the helmet of the still A is substituted a cylindrical vessel, B, with an opening in the bottom. The materials to be distilled are brought into B, and rest upon a wire bottom to prevent particles from falling into A. From the upper portion of B a pipe, R, leads to the condenser. As may be seen from the illustration, the still A serves only for the generation of steam. The latter, in passing through B, heats the contents and absorbs the liberated oil, the combined vapors passing into the condenser.

This simple modification of the ordinary still affords some advantage, the principal being the avoidance of the condensation of a large quantity of water. This in itself would not amount to much, but it has to be taken into consideration that, though volatile oils are only very sparingly soluble in water, they are nevertheless soluble in it to such a degree as to impart to it their characteristic odor and taste. Such aromatized water can be utilized in the manufacture of liqueurs and perfumery, but to the manufacturer who restricts himself to the production of volatile oils alone, this represents a loss, and it is therefore necessary for him to condense as little water as possible. And this object can only be attained by the use of direct steam.

A simple apparatus for the purpose is shown in Fig. 5. The still b, provided with a helmet, rests free upon a suitable support. To prevent cooling, it is surrounded with a wooden jacket, M. The material to be extracted rests upon a perforated bottom, beneath which enters the pipe HD, which conducts the steam from the boiler. For the more uniform distribution of the steam, it is recommended to let this pipe end in a perforated coil. The water condensed in the apparatus itself is discharged through the short pipe H, placed in the lowest part of the still.

An improved apparatus for distilling dry substances by steam has been patented in Germany by Messrs. Schimmel & Co., of Leipzic. The tall conical column at the left (Fig. 6) is the still. About eight inches from the bottom is a perforated diaphragm or false bottom, upon which the material to be distilled is placed by introducing it through the still-head. A perforated coil below the diaphragm projects steam upwards through the mass, which is occasionally agitated from without by means of a horizontal stirring apparatus indicated by the two crosses. Any condensed water which may run back is converted into steam by the heating coil at the bottom. Meanwhile, the mass itself is heated by a long coil lining the body of the still and carrying steam at a high pressure. Whatever of volatile oil is carried forward by the steam passes through the still-head into the cooler on the right, where both oil and steam are condensed, and from where they flow through a small funnel tube into three successive receivers, which are arranged like Florentine flasks, and which retain the volatile oil that has separated. From the last receiver the water, which is still impregnated with oil, enters another reservoir, shown in the illustration only by dots, and from there it flows into a small globular still situated underneath; in which, by means of steam, nearly all the oil still retained is again volatilized with the steam of the water and both again conducted to the cooler.

Attempts have been made to effect the distillation of volatile oils without the use of steam by means of hot air, but comparative experiments have shown that less oil is obtained. With the use of steam, the vegetable substances swell up by the absorption of water, and thus afford a free passage to the oil, liberated from the sacs containing it. With the use of hot air, on the other hand, the surface of the plant is completely dried and shrivels to a hard solid mass, which offers considerable resistance to the process of distillation.

This injurious effect of hot air can be somewhat overcome by thoroughly moistening the plants to be distilled, and allowing the hot air, before entering the still, to pass through a pipe filled with sponges constantly kept wet. But this process offers no advantages over that by steam. The apparatus required is far more complicated; and, besides, a ventilator has to be provided for forcing the hot air through the apparatus.

Separation of the oil and water.—As previously mentioned the specific gravity of most volatile oils is less than that of water. This behavior is utilized for the separation of the oil and water, by means of a so-called Florentine flask (Fig. 7). It consists of a glass flask provided near the bottom with a pipe, a, rising vertically to near the neck c of the flask where it is bent downwards as shown in the illustration. The mixed liquid of water and oil drips from the cooling pipe into the flask, and the water w, being specifically heavier, separates from the oil floating on the top, and gradually ascends in the pipe a, finally flowing over at d. Oils specifically heavier than water are caught in receivers provided with a discharge-pipe near the mouth of the flask as shown in Fig. 8.

The oil delivered from the receivers is, however, still mixed with some water, dirt, etc., and for their separation is allowed to stand quietly for some time. The final separation is effected either by simply pouring off the oil, especially if larger quantities have to be handled, or with the assistance of a separator-funnel (Fig. 9). This consists of the glass-funnel T secured to the stand G, and provided with a close-fitting lid, P. The fluid is poured into the funnel, the lid placed in position, and the whole allowed to rest until the water W is completely separated from the oil O. The oil is then separated from the last drops of water by carefully opening the faucet H.

Most volatile oils are obtained by distillation, but this method is not practicable for separating the odoriferous principle of many of the most sweet-scented and delicate flowers, partially because the flowers contain too little oil, and partially because the oil would lose in quality if obtained by distillation.

Extraction.—For obtaining the volatile oils by extraction various solvents such as ether, bisulphide of carbon, etc., may be employed. Carefully rectified petroleum-ether is very suitable for the purpose. It completely evaporates at about 122° F., and when sufficiently purified does not possess a disagreeable odor. The process of extraction is briefly as follows: The material to be extracted is treated in a digester with petroleum-ether or one of the above-named solvents. The solution is then drawn off and the solvent evaporated in a still. The recondensed solvent flows immediately back into the digester and further extracts the material contained therein. The operation is repeated until nothing soluble remains. In practice some difficulties are, however, connected with this process since, besides the volatile oils, resins, and coloring and extractive substances are dissolved, which have to be removed, as well as the last traces of the solvent, as otherwise the oil would acquire a foreign odor. Further the solvents mentioned are very volatile and inflammable, requiring the greatest precautions as regards fire. For these reasons the extraction process is not suitable for many purposes, and though at first great hopes were entertained in regard to it, its use is limited to substances with a large content of volatile oil.

For extraction on a small scale, the apparatus, Fig. 10, is a very suitable one. It is especially adapted for manufacturers of perfumery, who wish to extract fresh flowers. It consists of a cylindrical vessel, C, of tin plate, provided on the bottom with the stop-cock a and the pipe b. The lid D fits into a gutter, R, running around the edge of C, and is hermetically closed by water in R. The cylinder is filled with the vegetable substance to be extracted, and sufficient petroleum-ether or bisulphide of carbon to cover it, poured in. The lid is then adjusted, the gutter R filled with water and the apparatus allowed to stand quietly for forty minutes. To remove the fluid from the cylinder, the faucet o in the lid is first opened, and then the stop-cock a; the fluid escapes at b, and is caught in a well-closed vessel. The operation may be repeated once or twice, or the vegetable substance is pressed out by means of a wooden plate, and the apparatus filled anew. The faucet h serves for emptying the gutter R.

Extraction being finished, the cock o is opened, and then the cock a, and the fluid allowed to run into the flask of the distilling apparatus (Fig. 2). For working on a large scale, the flask is, however, too small, and is suitably replaced by a bottle-shaped tin vessel, F (Fig. 11), the conical cover D of which is secured by means of the rubber ring R and iron screw-clamps, S. A bent glass tube fitted into the cover is connected with the cooling-pipe of the apparatus shown in Fig. 2. But the oils prepared by extraction are not sufficiently purified by mere rectification, as traces of the solvent adhere tenaciously to them, which can only be removed by passing a current of air through the oil. But contact with air has an injurious effect upon the delicacy of the odor. For expensive oils a current of air should therefore never be used, but one of pure carbonic acid. Fig. 12 shows a suitable apparatus for the purpose. The large bottle A, filled half full with pieces of white marble, is closed with a doubly-perforated cork; through one of the holes is inserted a funnel-tube, and through the other a short tube bent at a right angle. The latter is connected with another tube which reaches to the bottom of the vessel B, in which is also inserted a tube open in the bottom, and a short tube bent at a right angle. Alongside B stands another vessel, C, arranged in the same manner. The tube leading from C is connected with a tin pipe, D, with a rose-like expansion on its lower end. This pipe is inserted in the glass balloon containing the volatile oil. Finally, a pipe leads to the flask F, filled with water.

To put the apparatus in operation, strongly diluted hydrochloric acid is poured through the funnel-tube upon the pieces of marble in A, which causes the development of a current of carbonic acid. But as the latter carries along water and hydrochloric acid, it has to be freed from them before coming in contact with the volatile oil. The vessels B and C serve for the purpose. B is half filled with water, while C contains strong sulphuric acid. In B the hydrochloric acid carried along with the current of carbonic acid is retained, while the water is fixed on the sulphuric acid in C. The current of carbonic acid passing out from C is perfectly pure, and enters the volatile oil through the fine perforations in the pipe D. It absorbs the traces of solvent still adhering to the oil, and finally passes out through the water in the bottle F.

Volatile oils obtained by extraction, and purified by a current of carbonic acid, will keep for years without undergoing alteration, if placed immediately in hermetically closed vessels and stored in a dark place. Oils purified by a current of air always become somewhat thickly fluid by storing, and partially lose their fine odor, which is due to the oxygen absorbed during the process.

For the extraction of oil on a larger scale, the apparatus shown in Fig. 13 is very suitable. It consists of two principal parts, the actual extracting vessel E, and the still B. The extracting vessel E sits in a vat containing cold water, W, the arrangement being such that the heated water can be removed and replaced by cold. The still B sits in a boiler, K, filled with hot water.

The apparatus is charged as follows: The conical head C of the extracting vessel E is unscrewed and its connection at H with the pipe R loosened. The extracting vessel is then charged with the vegetable substance, the head C replaced, and the connection with the pipe R restored. The cocks H₂ and H₄ are then opened, and the required quantity of solvent is brought into the still. Both cocks are then closed, and the cocks H and H₁ opened. The water in the boiler is then heated until the contents of the still commence to boil. The vapor of the solvent ascends through the pipe R; on entering the extracting vessel E it is condensed, and after falling as a spray upon the material to be extracted, finally returns impregnated with volatile oil to the still B. Here the solvent is revaporized, and passes again through the material in the extracting vessel, while the extracted oil remains in the still. During the boiling of the solvent the extracting vessel must be suitably cooled by the constant admission of cold water.

When extraction is finished, the cocks H and H₁ are closed, and the cock H₂, which is connected with a cooling worm, is opened. The solvent is then evaporated, and regained by condensation. The oil is discharged, from the still through a pipe in the bottom provided with the cock H₃.

The apparatus may also be so arranged that the still B is connected with two extracting vessels which are used alternately, while the contents of one are being extracted the other is emptied and refilled.

For working on a very large scale, Heyl's extracting apparatus, shown in Fig. 14, is very suitable. It consists of a battery of four or more cast iron or sheet iron cylinders, A₁ to A₄, communicating with each other and surrounded by steam jackets. The extracting vessels are so arranged that they can be emptied by tilting, which is rather inconvenient, as all the pipes have to be unscrewed. In each cylinder close above the bottom is a perforated plate covered with fine wire-gauze, upon which the material to be extracted is placed. The cylinder is filled to the top, and, after placing a similar plate upon it, the upper opening is closed by a lid suspended to a crane. The cylinder, as well as the lid, is provided with a broad flange, between which is placed a hemp tissue firmly pressed together by 12 clamps to serve for packing. After filling the cylinders with the material to be extracted and arranging the packing, the solvent (bisulphide of carbon) is conducted from a reservoir through the principal pipe, B, to the extracting vessels, and is introduced into A₂ by opening the cock C₂, which communicates with the pipe B. The bisulphide of carbon passes through the bent pipe D₁, enters through the cock E₂, below the false bottom of the cylinder A₂, and, after penetrating the mass and filling the cylinder, runs through the cock C₂ of the bent pipe D₂, and the cock E₃ into the cylinder A₃, reaching the fourth cylinder in the same manner through the cock C₃, the pipe D₃, and the cock E₄. From the last cylinder it passes as a thoroughly saturated oil solution into a reservoir, in which a vacuum has been created to promote the circulation of the fluid in the entire apparatus. After a quantity of oil solution corresponding to the contents of the cylinder A₄ has arrived, the cock G₄ is closed and the cock C₄ opened, whereby the cylinder A₄ is connected with A₁ by the bent pipe D₄ and the cock E₁.

After the exhaustion of the contents of the cylinder A₂, which is recognized by means of the glass tube H₂ placed on D₂ by the fluid running off being colorless, the cocks C₁ and E₂ are closed, and C₂ and E₃ opened, whereby the solvent runs into A₃, and from there to A₄ and A₁; A₂ being omitted. To effect this omission, and at the same time not to prevent the introduction of bisulphide of carbon, C₁, C₂, C₃, and C₄, are so-called two-way cocks, which, when placed in one position, connect the principal pipe B with the branch pipes D, but interrupt a further flow through the principal pipe B; while in the other position they close the pipes D and open the principal pipe B.

The cylinder A₂ is, however, still filled with the solvent and material saturated with it. To remove the solvent, the discharge cock K₂ on the bottom of the cylinder is opened, which communicates with the discharge pipe J, through which the bisulphide of carbon is conducted into a reservoir. The discharge is promoted by opening the cock M₂, connected with the pipe L, and the admittance of compressed air, which displaces the liquid solvent. After the flow of the latter has ceased, the steam cocks on the jacket O₂ and the cylinder P₂ are opened under constant admission of air and simultaneous introduction of steam through the pipe N into the upper part of the cylinder.

The solvent (bisulphide of carbon) converted into vapor by the heat, is conducted together with the aqueous vapor, by the admission of air through the cock K₂, the pipe J, and a cooling pipe placed between the extracting vessels and the reservoir, and collected in a reservoir to be re-used.

On account of the great volatility of bisulphide of carbon, considerable loss would, however, be incurred by the above-mentioned admission of air. To avoid this, the reservoir serving for the reception of the condensed bisulphide of carbon and aqueous vapor is closed, and connected by a pipe with a long, narrow, horizontal cylinder half filled with oil, and provided with a fan-shaft. The vapors of bisulphide of carbon entering the cylinder from the reservoir are absorbed, together with the air by the oil, the surface of which is constantly agitated by the fan-shaft, while the air, rendered entirely inodorous, passes out at the other end. The bisulphide of carbon is finally separated from the oil by distillation and again used.

After the cylinder A₂ is sufficiently steamed, it is emptied and again charged with material and connected with the cylinder A₁; while the other cylinders undergo the same manipulations described above.

The saturated oil solution is subjected to distillation, which is readily effected in Heyl's apparatus, Fig. 15. The lower part of the still A of boiler plate is surrounded by the steam-jacket B, into which steam is admitted through C and the condensed water discharged through D. The concentrated oil solution runs from a reservoir, standing at a higher level through the pipe E into the still, the admission of a sufficient quantity being indicated by the gauge F. The bisulphide of carbon brought to the boiling point (114° F.) by the steam introduced into the jacket, vaporizes quickly; the vaporization being still more accelerated by revolving the stirrer H, by means of the crank G. The vapors of bisulphide of carbon escape through four openings in the upper part of the still, into a capacious worm, the lower part of which enters, under water, a reservoir.

Notwithstanding the volatility of bisulphide of carbon, the oil retains a portion of it so tenaciously that a complete separation cannot be accomplished by the introduction of steam into the jacket B. Hence, in order to vaporize the last traces of the solvent, air is introduced into the oil through the pipe K, the lower end of which is perforated. After completed distillation the oil is discharged through L.

Maceration or infusion.—This process is employed for flowers with an inconsiderable content of volatile oil or whose odoriferous substance would suffer decomposition or alteration by distillation. The process is founded on the affinity of odoriferous substances for fatty bodies which, when impregnated with them, are called pomades. These are afterwards made to yield the aroma to strong alcohol, so that finally there is obtained a solution of the volatile oil in alcohol from which the pure oil is obtained by distilling off the alcohol. The fat used, olive oil, lard, etc., should be entirely neutral, i. e., free from every trace of acid. The fats are purified by treating them several times in the heat with weak soda-lye and then washing carefully with water until the last traces of the lye are removed, and the fat shows no alkaline or acid reaction.

With the use of olive oil the so-called "Huiles antiques" are obtained, which are merely solutions of volatile oils in the fixed oil. By the use of lard, etc., the genuine pomades are obtained, which are directly used as expensive articles of perfumery, but in the factories serve as a starting point for the preparation of volatile oils.

The old process of maceration, which is still in use in some parts of France, is as follows: A certain quantity of fat is placed in an enameled iron or porcelain pan provided with a water or steam bath. When the fat is melted, the freshly gathered flowers from which the aroma is to be extracted are thrown in and left to digest for from twelve to twenty-four hours, the fat being kept fluid and stirred frequently. When the flowers are completely exhausted, the fat is strained from them into fresh pots, in which it is again macerated with fresh flowers as before. This operation is repeated ten to fifteen times until the pomade has acquired the desired strength.

Experience, however, has shown that volatile oils prepared by this process possess a finer odor the shorter the time the flowers remain in contact with the fat. Piver has devised an apparatus which reduces the time of maceration to the shortest period possible. The kettle to the left, Fig. 16, supplies the fat heated to the proper temperature, which circulates slowly through the macerating tank, in which a constant temperature of 149° F. is maintained by means of a steam pipe. The macerating tank is divided into compartments, in which baskets containing the vegetable substance to be extracted are suspended. The basket on the left contains the substance which has passed through all the compartments; it is from time to time removed, filled with fresh substance, and then attached to the right, the other baskets being moved to the next compartment to the left. In this way the fresh substance has to traverse each compartment from right to left, while the fat flows slowly from left to right, and saturated with the perfume of the substance collects in the tank on the extreme right.

Maceration is employed for the flowers of the orange (citrus aurantum), of the mock orange (Philadelphus coronarius), of the acacia (acacia Farnesiana), of the violet (viola odorata), of the mignonette (rÉsÉda odorata), etc.

The process of absorption, or "enfleurage," as it is called by the French, is chiefly made use of for procuring the odoriferous principle of very delicate flowers, the delicious odor of which would be greatly modified, if not entirely spoiled, by the application of heat. The older apparatus employed for the purpose consists of a number of shallow wooden frames of about 15×18 inches, inclosing at half their depth a sheet of glass. The edges of the frame rise about an inch above each surface of the glass, and, being flat, the frames stand securely upon one another, forming often considerable stacks. These frames are called "chassis," those just described being termed "chassis aux vitres," or "chassis aux pomades," to distinguish them from a different form, which is used where oil has to be submitted to the process of absorption. The process in the case of pomade is as follows: Each sheet of glass is uniformly coated with a thin layer of purified grease, care being taken that the grease does not come in contact with the woodwork of the frames. The flowers are then thinly sprinkled, or rather laid, one by one, upon the surface of the fat, where they are allowed to remain one or two days, when they are removed and replaced by fresh ones. The operation is thus continued for twenty-five or thirty days, until the fat is saturated with aroma. The frames charged with fat and flowers are stacked one upon the other, forming, in fact, a number of little rectangular chambers.

For perfuming oils a metal sieve, Fig. 17, is substituted for the glass plate. Upon the sieve a piece of thick cotton cloth saturated with oil is laid, and upon this the flowers are scattered, and left there until fresh ones have to be substituted. The operation is repeated until the oil is sufficiently impregnated with aroma, when the cloth is subjected to pressure and the expressed oil filtered.

This process is very tedious, requiring much labor and a long time for the impregnation of the fat or oil, but, notwithstanding its faults, it is still pursued to a great extent, some French firms using 3000 such frames during the season.

With the apparatus, shown in Fig. 18, the process of absorption can, however, be conducted with very little expense of labor and time. It has the further advantage that the flowers do not come in direct contact with the fat, whereby a saving of the latter is effected, and it is less liable to rancidity.

The apparatus consists of a tall wooden box provided with doors which can be hermetically closed. In the box are placed upon brackets a number of glass plates, g, so arranged one above the other that, for instance, those with uneven numbers are on the left side, leaving an open space to the right, while those with even numbers are arranged on the right side with an open space to the left.

From the bottom of the box a pipe passes into a sheet-iron cylinder, K´, filled loosely with flowers, and provided with lateral openings, O and O´. From the lid of the box K ascends a pipe, e, which is connected with a small ventilating apparatus kept in motion by a clockwork and weights. This ventilator when in motion sucks a current of air through the apparatus. The air enters the cylinder K´ at O, and after ascending through the flowers and becoming impregnated with the vapors of the volatile oil enters through the opening O´ into the box K and, in passing in the direction indicated by arrows, over the plates coated with fat, yields its aroma to them.

Another apparatus for the same purpose, devised by Piver, is shown in Fig. 19. The fat is converted into thin macaroni-like threads and brought upon wire gauze stretched in frames. The flowers to be extracted are piled upon tinned metallic plates, and the trays containing the fat and the flowers are placed in an air-tight chamber arranged as shown in the illustration. The air in the chamber is made to circulate to and fro by the working of a bellows with which the apparatus is provided, whereby the fat is caused to absorb the odor of the flowers very rapidly and is less liable to rancidity.

The absorption process is employed for the flowers of the jasmine (jasminum oderatissimum), the mignonnette (rÉsÉda odorata), the violet (viola tricolor), the tuberose (polianthes tuberosa), etc.

Storage of volatile oils.—In storing volatile oils, they should be carefully protected from light and air. Some oils become darker on exposure to light, while others, for instance, lemon oil, become colorless. Most volatile oils, as previously mentioned, absorb oxygen from the air with avidity and combine chemically with it. Thinly-fluid oils become perceptibly more thickly-fluid and finally even rigid, the product of oxidation being a resinous body. Some volatile oils containing aldehydes are converted, by the absorption of oxygen, into acids, cinnamic acid being, for instance, formed in cinnamon oil, and benzoic acid in oil of bitter almonds.

To prevent evaporation, as well as the above-mentioned effects of light and air, the volatile oils should be preserved in not too large glass bottles kept as full as possible, and closed with a good cork, over which it is best to tie a piece of bladder. The bottles should be stored in a cool, shady place. The preservation of the oils is assisted by the addition of 0.5 to 1 per cent. of anhydrous alcohol.

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