There are three kinds of olive oil in the market. The best, called virgin salad oil, is obtained by a gentle pres sure in the cold,- the more common sort is procured lay stronger pressure, aided with the heat of boiling water; and thirdly, an inferior kind, by boiling the olive residuum, or mare, with water, whereby a good deal of mucilaginous oil rises and floats on the surface. The lat ter serves chiefly for making soaps. A still worse oil is got by allowing the mass of bruised olives to ferment before sub jecting it to pressure.
Oil of olives is refined for the watch makers by the following simple process Into a bottle or vial containing it, a slip of sheet lead is immersed, and the bottle is placed at a window, where it may re ceive the rays of the sun. The oil by degrees gets covered with a curdy mass, which after some time settles to the bot tom, while itself becomes limpid and colorless. As soon as the lead ceases to separate any more of that white sub stance, the oil is decanted off into another via] for use. • Palm oil melts at 117.5° F., and is said to consist of 31 parts of stearine and 69 of oleine in 100. It becomes readily ran cid by exposure to air, and is whitened at the same time.
The oil extracted from the plucked tops of the pins* abies, in the Black For est in Germany, is limpid, of a golden yellow color, and resembles in smell and taste the oil of turpentine. It answers well for the preparation of varnishes.
Poppy-seed oil has none of the narcotic properties of the poppy juice. It is solu ble in ether in every proportion.
Rape-seed oil has a yellow color, and a peculiar smell. At 25° F. it becomes a yellow mass, consisting of 46 parts of stearine, which fuses at 50°, and 54 of oleine, in which the smell resides.
The sun-flower is largely cultivated in this country, for the sake of the oil. An acre yields from 60 to 75 bushels, and every bushel gives a gallon of oil. The oil-cake is a fine fattener for cattle.
Oil of almonds is manufactured by agi tating the kernels in bags, so as to sepa rate their brown skins, grinding them in a mill, then enclosing them in bags, and squeezing them strongly between a series of cast iron plates, in a hydraulic press; without heat at first, and then between heated plates. The first oil is the purest, and least apt to become rancid. It should be refined by filtering through porous paper. Next to olive oil, this species is the most easy to saponify. Bitter al
monds, being cheaper than the sweet, are used in preference for obtaining this oil, and they afford an article equally bland, wholesome, and inodorous. But a strongly scented oil may he procured, according to M. Planch5, by macerating the almonds in hot water, so as to blanch them, then drying them in a stove, and afterwards subjecting them to pressure. The volatile oil of almonds is obtained by distilling the mare or bitter almond cake, along with water.
Linseed, rapeseed, poppyseed, and other oleiferous seeds were formerly treated for the extraction of their oil, by pounding in hard wooden mortars with pestles shod with iron, set in motion by cams driven by a shaft turned with horse or water power, then the triturated seed was put into woollen bags which were wrapped up in hair-cloths, and squeezed between upright wedges in press-boxes by the impulsion of vertical rams driven also by a cam mechanism. In the best mills upon the old construction, the cakes obtained by this first wedge pres sure were thrown upon the bed of an edge-mill, ground anew and subjected to a second pressure, aided by heat now, as in the first case. These mortars and press-boxes constitute what are called Dutch mills.
A good oil for chronometers is a great desideratum. The following has been tried, and is mach used :—Having pro cured good olive oil, 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 .n it; and, when the temperature rises to 920°, 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 eva porated. The oil is then exposed to a temperature of 80° to 86°, for two or three days. 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 re-dis solved, may be used for common pur poses. Lastly, the fluid portion must be filtered, once or more, through newly prepared animal charcoal, grossly pow dered, 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 colorless.