An apparatus recently constructed by Rigaud and Dussart is arranged so that dry steam enters directly among the matters to be distilled, and the temperature is always maintained at a high point. This is shown in Fig. 1042. It is claimed to yield a larger and superior product, and to prevent all chance of creating an empyreumatio odour, such as sometimes happens with other forms.
Distillation as a means of obtaining essential oils is worthy of every consideration. Generally it should be effected by steam ; but there are cases (bitter almonds, &c.) where contact with water is necessary for the production of the oil, while in others, open fire and steam are equally appli cable, though the latter is superior. The water employed must be perfectly pure and neutral, though in some cases (sassafras, cloves, cinnamon, &c.), common salt is added to raise the boiling-point. The receiver is always some form (there are many) of " Florentine receiver." In some instances (anise, &c.) where the distillation-products are solidifiable at a low temperature, the condenser-worm needs to be warmed instead of cooled.
Maceration.—Some of the most delicately perfumed essential oils are spoilt by distillation ; these are ex tracted by maceration in previously clarified solid fats or fixed oils. The grease to be perfumed is melted in a water-bath, and the flowers are thrown in, and allowed to remain for 24-48 hours, when they are withdrawn, freed from grease, and replaced by others, the operation lasting perhaps 15 days, and the product being numbered 6, 12, 18, 24, according to the amount of fragrance it has absorbed. Difficulties encountered in the conduct of the operation are the possible extraction of the colouring and other principles from the flowers, and the decompo sition of the perfume and rancidifica tion of the grease, by the repeated alternation of heat and cold. To obviate these drawbacks, Fiver has introduced the saturator shown in Fig. 1043. This enables some 2100 lb. of grease, contained in 7 compartments, to be saturated in one day ; the grease overflows by a spout leading from one compartment to another at the bottom, being kept in a liquid state by a water-bath meanwhile. Boxes of wire gauze carry the flowers, and advance in a contrary direction to the grease, each entering No. 7 and finally leaving No. 1 quite exhausted. This opposite passage brings the virgin oil into contact with the flowers which are nearly exhausted, while the already partially impregnated grease readily absorbs some of the excess of essential oil from the fresh flowers.
Relining, Clarifying, and various processes under this bead may at first be broadly divided into " mechanical" and " chemical," although each, especially the hitter, is capable of many subdivisions. They have for their object, firstly, the removal of all extraneous matters from the oil (using this term to include melted fats, as well as oils fluid at the ordinary temperature, since almost all these operations are conducted upon fluids), such as animal or vegetable fibre and tissue incidental to the modes of preparation (as in olive- and other seed-oils, badly-rendered tallow, &c.) ; secondly, of resinous substances dissolved in the oil,
of which the refining of cotton-seed-oil is a notable example ; thirdly, the removal of fraudulent admixtures, such as lime, glue, &c.; fourthly, the correction of rancidity ; and fifthly, where the preceding operations do not sufficiently improve the colour of the oil, its bleaching by chemical processes. These will now be considered under their various heads, and it is obvious that much care and judgment are required in the selection of the particular method or combination of methods suitable to the refining of any given oil.
The first and most important method, to be employed either alone, or as a sequel to others, is that of simple but prolonged subsidence, on a large scale. Where necessary, the tanks employed may be heated by steam-coils or steam-jackets. These must be used with caution, however, since con vection currents are set up, which interfere materially with the deposition of impurities. An obvious modification of this method is filtration, which may be effected io a very great variety of ways, either with or without the assistance of artificial pressure derived from (a) a " head " of the liquor to be filtered, (b) one of the many forms of filter-press in use, or (e) atmospheric pressure, by the production of a vacuum under the filter-bed (see p. For example, alive-oil is mostly subjected to no process of purification, beyond what is attained by allowing it to deposit impurities, and repeatedly decanting. But for the best qualities, further purification is necessary, not only to secure limpidity, but a capacity for lengthened preservation, by eliminating the water, mucilage, and parenchymatous matters. Various devices are employed in different localities, one and all being filters. In France, the oil to be purified is received into perforated boxes carpeted with carded cotton (wadding); elsewhere, cotton tissue interposed between beds of granular and washed animal charcoal form the filter ; also a bed of dry moss, on the Grouvelle et Jaunez ' system ; also layers of sand, gypsum and coke ; also alternate beds of sand and vegetable charcoal, according to Denis de Montfort's plan ; also carbonized schist and peat, by Cossus' method ; also clay heated to 200° ( ? F.), as proposed by Wright ; also by introducing China-clay and allowing to stand at a moderate temperature, then filtering through cotton, as adopted by A. Bizzarri. Perhaps the best mode is that of Pietro Isnardi, of Livornia, Tuscany, which received an award at the Vienna Exhibition. This apparatus, Fig. 1044, consists of a boiler full of water, serving as a water-bath for two turned-iron cylinders b, receiving the oil from the reservoir c, a suction- and force-pump d, and a filter e, containing per forated trays whose holes are filled with wadding. This apparatus enables the oil to be filtered without coming into contact with the air, and at an elevated temperature which can be regularly maintained. Coco-nut-oil is another example of purification by simple subsidence and filtration.