A practical treatise on the manufacture of perfumery

by C. Deite

Another method of expressing the oil is that of the écuelle à piquer, much used in the region about Nice. The oils obtained by this method, which are also of a very fine quality, are marked essence à l'écuelle or au zeste. The apparatus consists of a round shallow pan of copper or brass, having a receptacle for the oil at its lowest part and a lip on one side for pouring, and studded on its concavity by strong blunt spikes. The workman takes the fruit and rolls it gently but quickly around the inside of the écuelle; the spikes prick the oil sacs, whereupon the oil, running down the spikes and the concavity of the pan, collects in the reservoir at the lowest part. The oil is filtered and then poured into clean glass bottles, in which the impurities are allowed to settle.

In Reggio, where especially much bergamot oil is manufactured, sheet-metal bowl-like vessels, studded inside with sharp ribs, are used. Six to eight fruits are placed in the vessel. A movable lid closes the vessel, so that there is just enough space for the fruits between the lid and the bottom of the vessel. If now the lid be revolved by hand-or steam-power, the rinds of the fruit are torn apart, and the oil together with the juice runs through the sieve-bottom of the apparatus into a cylindrical vessel where it clarifies.

The third method of obtaining the oil is by expression. The grated rind is placed in hair mats, and subjected to powerful pressure by means of a screw or lever press.

The process of distillation is carried on as follows: The peels, which should be from select fruit, are sprinkled with powdered salt, and a few hours afterwards sufficient water to moisten them is poured over them. A day or two afterwards more water is added, and the whole is distilled until either no more oil separates or the steam, at first purely fragrant, begins to acquire a rank and rather unpleasant smell. The oil obtained by distillation is inferior to the others.

Fig. 20.

Lately a combination of the écuelle and distilling processes has been introduced by Domenico Monfalcone, which has given excellent results. It is shown in Fig. 20. F F is a hollow cylinder, of sheet-iron, the interior surface of which is studded with a large number of small metallic knife-points. This cylinder revolves on two axles attached to it at diagonally opposite points. The cylinder having been half-charged with lemons, together with a small quantity of water, is set in motion by aid of the shafting and pulleys driven by the small steam engine. The fruits are thereby made to come in contact with the metallic lancets, and their whole surface gradually becomes punctured sufficiently to rupture the cells containing the volatile oil, which escapes. The cylinder F F has double walls, the space between them being intended for the circulation of a current of steam, which is admitted to heat the water and to facilitate the extraction of the oil, while at the same time the vapors are rarefied or aspirated by the vacuum pump L. The axles of the cylinder on both sides are hollow; that on the side looking towards the engine is imbedded in such a manner that steam from the boiler D may be admitted at will, either into the double walls of the cylinder, or into the interior of the cylinder itself, while the hollow passage in the other axle communicates with a condensing worm, G, the outlet of which, H, descends into a cylindrical vessel, I, intended to receive the condensed products, consisting of water and volatile oil. When the apparatus is first set in motion the pump L begins to produce a vacuum during the first revolutions of the cylinder. Steam being now cautiously admitted into the double walls of the cylinder, the water is raised to boiling at a comparatively low temperature, and the vapors charged with the volatile oil pass over into the receptacle, where they separate into two layers. The product obtained by this process is claimed to be equal in quality to that obtained by mechanical means, and the yield nearly double.

During the months of November to March the average yield from 1000 lemons in the factories of Palermo is 320 grammes of oil; in those of Messina, where a better quality of fruit is employed, the yield is about 400 grammes. The same number of lemons yield about 10 gallons of juice, the collection of which is, of course, a necessary accompaniment of the manufacture of volatile oil.

Pure oil of lemons is almost colorless and has the odor of the fruit. Its specific gravity varies between 0.8752 and 0.8785; it boils at 298.4° F., and is soluble in all proportions in absolute alcohol and glacial acetic acid. It contains, according to G. Bouchardat and J. Lafont, besides a little cymene, several hydrocarbons, the most abundant of which is citrene, C₁₀H₁₆, boiling near 352.5° F., having a rotatory power exceeding +105°, and yielding a solid optically inactive dihydrochloride.

Oil of lemons is frequently adulterated with oil of turpentine. This may be detected, according to G. Heppe, by slowly heating the oil in a dry test-tube with a small piece of copper butyrate to about 338° F., taking care that the temperature does not exceed 356°F. The copper salt will dissolve in pure oil of lemons with a green color, while in the presence of oil of turpentine a yellow turbid mixture is obtained, reddish-yellow cuprous oxide being separated. This test is also applicable to oils of bergamot and of orange-peel.