Extraction.
This method is based on the fact that some volatile liquids such as ether, chloroform, petroleum ether, or bisulphide of carbon possess the property of rapidly extracting the aromatic substances from flowers; when they are evaporated at a gentle heat they leave the pure odors behind. In our opinion this process is the best of all for the perfumer and it is to be regretted that it is not more generally used.
As a rule we employ either petroleum ether or bisulphide of carbon (see above, pp. 65, 66) because these products are cheaper than ether or chloroform.
The apparatus we use for this purpose is illustrated in Fig. 21. It consists of a cylinder C made of tinned iron, which is provided above with a circular gutter R terminating in a stop-cock h and which can be closed by a lid D bearing a stop-cock o. A tube b with a stop-cock a enters the bottom of the cylinder. The latter is filled with the flowers, the volatile liquid (petroleum ether, bisulphide of carbon, etc.) is poured over them, the lid is put on, and the gutter R filled with water, thereby sealing the contents of the vessel hermetically.
After the extraction, which requires about thirty to forty minutes, stop-cock o is opened first, then stop-cock a, and the liquid is allowed to escape into the retort of the still (Fig. 12). If the extraction is to be repeated, the water is allowed to escape from the gutter through h, the lid is opened, and the solvent is again poured over the flowers.
For operation on a larger scale the glass retorts are too small and should be replaced by tin vessels (Fig. 22) having the form of a wide-mouthed bottle F; they are closed by a lid D which is rendered air tight by being clamped upon the flange of the vessel (R) with iron screws S, a pasteboard washer being interposed; a curved glass tube connects the apparatus with the condenser of Fig. 12.
Fig. 21. Fig. 22.
The solutions of the aromatic substances are evaporated in these apparatuses at the lowest possible temperature, the solvent being condensed and used over again. The heat required is for ether about 36° C. (97° F.), for chloroform about 65° C. (149° F.), for petroleum ether about 56° C. (133° F.), and for bisulphide of carbon about 45° C. (113° F.). If it is desired to obtain the aromatic substances pure from an alcoholic extract of the pomades made by one of the above-described processes—which is rarely done since these solutions are generally used as such for perfumes—a heat of 75 to 80 C. (167 to 176° F.) is required.
Another extraction apparatus illustrated in Fig. 23 is well adapted to operations on a large scale. Its main parts are the extractor E and the still B. The former is set in a vat W continually supplied with cold water. The still B is surrounded with hot water in the boiler K.
Fig. 23.
To start the apparatus the cone C is removed, the vessel E is filled with the material to be extracted, and C is replaced. The faucets H2 and H4 are opened, the solvent is poured into the still through the latter, when these faucets are closed and those marked H and H1 are opened.
The water in K is heated until the contents of B are in brisk ebullition; the vapor rises through RH, is condensed on entering E and falls in small drops on the material. This fine rain of the solvent dissolves the aromatic substances and flows back into B, where it is again evaporated, and so on.
At the end of the extraction the faucets H and H1 are closed and H2, is opened. The vapors of the solvent pass through it into a worm where they are condensed; the essential oil remaining in B is drained off by opening H3.
For still larger operations more perfect apparatuses are employed, such as those of Seiffert and Vohl. Seiffert’s apparatus (Fig. 24) consists of a battery of jacketed cylinders; steam circulates in the space between the cylinders and the jackets. Each cylinder contains a plate covered with a wire net on which the flowers to be extracted are placed. All the cylinders having been filled and closed, the solvent is admitted from a container above, through S and a into C2; when this is filled the liquid flows through a2b3cn into C. The solution saturated with essential oil leaves the apparatus through dn and p and enters a reservoir. The course of the liquid is aided by the suction of an air-pump acting on p.
When the reservoir contains an amount of fluid equal to that in Cn, dn is closed, an is opened, and C connected with C1 through bn and c1. That the contents of C2 are completely extracted is shown by the fact that the liquid appears colorless in the glass tube inserted in b2; a1 and C2 are closed; a2 and C3 are opened, thereby excluding C2 from the current of bisulphide of carbon which then flows through C3CnC1. In order to permit the free flow of the bisulphide of carbon through S despite the exclusion of C2, the faucets a1a2a3an must be two-way cocks; in one position they connect S with b; in the other they close b and leave the passage through S open.
Fig. 24.
In order to collect the bisulphide of carbon present in the extracted residue in C2, faucet g2 is opened and the bisulphide of carbon allowed to escape through h. The faucet e2 in tube L on being opened admits compressed air to C2, thus hastening the outflow. If nothing escapes below, faucets f2 and fx are opened, steam enters through tube D between jacket and cylinder; the bisulphide of carbon vapor passes through g2 and h into the worm. After the expulsion of the bisulphide of carbon, C3 is emptied, refilled, connected with C1, and bisulphide of carbon admitted from C3 in the manner above described.
Fig. 25.
An extraction apparatus which has been much recommended of late is the so-called “Excelsior Apparatus” made by Wegelin and Huebner, Halle a. S., which can be worked with any desired solvent. The construction of the apparatus (Figs. 25 and 26) is as follows.
Fig. 26.
The solvent is admitted to the reservoir R in the lower part of the condenser B through the tube indicated in the figure. The material to be extracted having been filled into the cylinder A through the manhole, the apparatus is closed. The cold water is admitted to the condenser by opening a faucet. The three-way cock shown in Fig. 25 is so placed as to open a communication of the overflow tube with A. The faucet at the lower end of the reservoir R is now opened sufficiently and the solvent passes into A from above, and as it descends takes up more and more oil, flows through the sieve-plate, and escapes through the tube at the bottom of A through the three-way cock, the overflow tube, and the drain tube into the accumulator C. The opening of a faucet now admits steam to the heating coil, when the solvent evaporates, leaving the oil or fat behind. It is condensed in B, again returns to R, whence it passes once more through the faucet into the extractor A. The vessel C and the tubes leading to A and C are surrounded with felt to prevent loss of heat. A sample taken from the small cock at the foot of A (it has a small plate in the interior of the tube) will show when the extraction in A may be looked upon as finished. The solvent is distilled off or recovered from the residue in A in the following manner. First the faucet in R is closed. The three-way cock A is set to establish direct communication between A and C, thus cutting off the overflow tube. Hence all the solvent in A flows into C for distillation, while the oil is left behind. Steam being admitted to the residue, the solvent rises as vapor through the upper tube from A to B and collects in a liquid state in R. To drive off the last traces of the solvent from the fat or oil obtained, steam is blown into C by opening the valve. Besides the solvent, watery vapor enters B and forms a layer of water in R under the solvent. By taking a sample from the test-cock of the reservoir C which has an internal small plate, the termination of the process is ascertained. The gauge tube at the reservoir shows the level of the solvent and water. The water is drawn off by opening the faucet at the lower end of the reservoir. A is emptied through the manhole and by draining the oil from C through the discharge cock. The tube R is closed by a light valve so as to prevent evaporation of the solvent. All the apparatuses work without pressure so that there is no danger from overstrain.
Fig. 27.
The solutions of the essential oils in bisulphide of carbon are distilled off in the steam still illustrated in Fig. 27; the steam enters at h, the water of condensation escapes at d, the liquid to be distilled enters at e from a container at a higher level. The boiling is kept uniform by the stirring arrangement hg. After the bisulphide of carbon is distilled off, air is passed through the oil by the curved tube a which has fine perforations, so as to evaporate the last traces of the solvent.
Fig. 28.
In Vohl’s apparatus (Fig. 28), arranged for petroleum ether, the extraction is effected with the boiling fluid; hence this apparatus is better adapted for the cheaper oils than for the finest oils from flowers. The apparatus consists of two extractors A A, the accumulator B, and the condenser C. Petroleum ether is allowed to flow over the substances to be extracted, by opening the faucets mm, vh, closing ogwE, and opening o, the course being through ux to B. When B is two-thirds full, the flow of petroleum ether is cut off, steam is admitted through y and the contents of B are brought to the boiling-point. The vapors pass through g and are condensed in f until the contents of A reach the boiling-point of the solvent, when the vapors pass through i into C, and after closing m´ the liquid passes through ml into the inner cylinder of the extraction apparatus and returns through uxx.
Fig. 29.
After the contents of A are extracted, m´ is opened, m closed, and steam is admitted through d into the jacket of A; the vapors of the solvent force the liquid part of the contents through ux into B. Overfilling of B is prevented by allowing the vapors of the solvent to escape at the proper time into the condenser through p by opening q. Then v is closed, q opened, and the steam present in A drawn off by an exhaust applied to p; as soon as p begins to cool, all the petroleum ether is distilled off, the steam is cut off at d, and the extract evacuated through t. The contents of B are brought into a still through D and E.
By employing greater pressure the extraction can also be effected by what is called displacement; the material to be extracted is placed in a stout-walled vessel S (Fig. 29) which is connected by a narrow tube at least ten yards long with the vessel F containing the solvent. Stopcock H is first opened, then stop-cock H1 which is closed as soon as fluid begins to flow from it. After the liquid has remained in contact with the material for from thirty to sixty minutes, H1 is opened very slowly, the liquid is allowed to escape and is displaced with water which is made to pass out of F in the same way as the solvent, until the latter is completely displaced from S.
After the solvent has been distilled off, the less volatile essential oil remains in the still almost pure, containing only traces of wax, vegetable fat or coloring matter which are of no consequence for our purposes. The last remnants of the solvent cannot be expelled by distillation, but by forcing through the essential oil a current of pure air for fifteen or twenty minutes. The essential oils then are of the purest, unexceptionable quality.
Fig. 30.
In the case of delicate oils it is better to use carbonic acid in place of air for expelling the last traces of the solvent, as the oxygen may impair the delicacy of the fragrance. For this purpose we use the apparatus illustrated in Fig. 30. In the large bottle A carbonic acid is generated by pouring hydrochloric acid over fragments of white marble. The carbonic acid passes into the vessel B filled with water which frees it from any adhering drops of hydrochloric acid; then into C filled with sulphuric acid to which it yields its water so that only pure carbonic acid escapes through the fine rose at the end of tube D which is made of pure tin, and as it passes through the oil in E it carries off the last traces of the volatile solvent. In its final passage through the water in F it leaves behind any oil that may have been carried with it.
As all the aromatic substances change in air by the gradual absorption of oxygen, and lose their odor—become resinified—these costly substances must be put into small bottles which they completely fill, and be preserved in a cool dark place, as light and heat favor resinification. The bottles must be closed with well-fitting glass stoppers.
Aromatic waters or eaux aromatisées, such as jasmine water (eau de jasmin), orange-flower water (eau de fleurs d’oranges, eau triple de Néroli, aqua naphæ triplex), etc., are made by distillation of these flowers with water and show a faint but very fine odor. When they contain, besides, dilute alcohol they are called spirituous waters or esprits. Those brought into commerce from southern France are of excellent quality.