Mr. Robinson, of Edinburgh, having witnessed the difficulties and waste which take place in filtering and clearing oil from its dregs; in which operation, as it is usually conducted, a great deal of the advantage which is gained by repose and subsidence, is again lost in drawing off the oil to pass it through the filter, it appeared to him that by introducing water through a regulated aperture, and from a height sufficient to give the requisite hydrostatic pressure into the bottom of the butt of oil, and making a communication from the top of a butt, to a filter acting by ascension, all the advantages arising from refuse and subsidence would be retained, and by adapting the nature of the filter to the quality of the oil, the contents of any butt might be easily and quickly separated into three or four portions of different degrees of value. Mr.. Robinson concludes by suggesting the mechanical arrangement, represented by the section of the apparatus in p. 200. n is a cistern of water which communicates by the pipe a with the bottom of the butt of oil g. f is the filter raised on feet, and standing on the heading of the butt, with which it communicates by the pipe b. e is a perforated plate above the lower chamber of the filter, and k is its discharging cock; c is the middle chamber filled with charcoal, or any other suitable substance.
The partition between this and the upper chamber d, is a perforated plate, and l is the discharging pipe of that chamber. The butt containing the oil being connected with the apparatus already described, the cock of the pipe a is to be turned, which will allow the water to flow into the butt. At the same time the cock of the pipe b being opened, the upper part of the oil, and therefore the purest, first flows into, and fills the lower chamber of the filter, and is followed by the less pure portions, according to their respective specific gravity; but as the pipe enters this chamber at the top, those impurities that are considerably heavier than the oil will subside to the bottom, and are from time to time to be discharged through the cock. The rest of the oil rises through the perforated plate, is separated from the lighter impurities by the charcoal or sand in the middle chamber, and then passes through the upper plate into the top chamber, whence it flows through the cock I. The two perforated plates must rest on rings or projecting ledges, that the charcoal may be renewed and the lower plate may be taken out occasionally, and cleared of the dregs which otherwise would stop its holes.
Under the words Elaine, and Fat, we have noticed the fine fluid oil that has received the former denomination, and which has been employed for lubricating delicate horological machinery. In this place, we have to describe an improved mode of obtaining it from olive oil by Mr. Henry Wilkinson, of Pall Mall, and which is considered to be peculiarly valuable for lubricating the pivots and other rubbing surfaces of chronometers. The best olive oil in its recent state, possesses that peculiar bland flavour which fits it for the table, and which appears to arise principally from the quantity of mucilage and water, either held in solution, or mechanically mixed with it. By keeping one or two years in jars, a considerable portion of the mucilage and water subsides, which renders such oil not only cheaper, but better qualified for yielding a greater proportion of pure oil than that which is recently expressed from the fruit. Two or three gallons skimmed from the surface of a large jar that has remained at rest for twelve months or upwards, is preferable to any succeeding portion from the same jar, and may be considered the cream of the oil.
Having procured good oil in the first instance, put about one gallon into a cast-iron vessel capable of holding two gallons; place it over a slow clear fire, keeping a thermometer suspended in it; and when the temperature rises to 220°, check the heat, never allowing it to exceed 230°, nor descend below 212°, for one hour, by which time the whole of the water and acetic acid will be evaporated; the oil is then exposed to a temperature of 30° to 36° for two or three days, (consequently winter is preferable for the preparation, as avoiding the trouble and expense of producing artificial cold); by this operation a considerable portion is congealed; and while in this state, pour the whole on a muslin filter, to allow the fluid portion to run through; the solid, when dissolved, may be used for common purposes. Lastly, the fluid portion must be filtered once or more, through newly prepared animal charcoal, grossly powdered, or rather broken, and placed on bibulous paper in a wire frame within a funnel; by which operation, rancidity (if any be present) is entirely removed, and the oil is rendered perfectly bright and colourless.
Under the article Candle, the reader will find accounts of several patented processes for obtaining the elaine, or pure oily principle, from the cocoa-nut, palm, and other concrete vegetable oils, so that we need not repeat them under the present head; but the extremely rude and ineffective machinery employed Dy the natives for expressing oils, in those countries from whence we derive our supplies, is worthy of the attention of the British reader, as exhibiting in a strong light the advantages that might result from the introduction of improved machinery in those parts. Dr. Davy informs us that the means used by the Singalese for this purpose, consists merely of a few upright poles stuck in the ground, supporting two parallel horizontal bars between them; between these, the bags: containing the seeds are put, in the manner represented in the subjoined sketch, pressure being given to the bags by means of a perpendicular lever which forces the horizontal 1 ars together. The native oil press employed at Madras, and other parts of the East, has somewhat more the character of a machine. The machine is large and substantial, and a great amount of animal force is wanted in operating by it.