The fat oils are completely insoluble in water. When agitated with it, the mix ture becomes turbid, but if it be allowed to settle, the oil collects by itself upon the surface. This method of washing is often employed to purify oils. Oils are little soluble in alcohol, except at high temperatures. Caster oil is the only one which dissolves in cold alcohol. 1:ther, however, is an excellent solvent of oils, and is therefore employed to extract them from other bodies in analysis ; after which it is withdrawn by distillation.
Fat oils may be exposed to a consider ably high temperature, without under going much alteration ; but when they are raised to nearly their boiling point, they begin to be decomposed. The vapors that then rise are not the oil itself, but certain products generated in it by the heat. These changes begin somewhere under of Fahr., and re quire for their continuance temperatures always increasing. The products con sist at first in aqueous vapor, then a very inflammable volatile oil, which causes boiling oil to take fire spontaneously ; and next carbureted hydrogen gas, with carbonic acid gas. In a lamp, a small portion of oil is raised in the wick by capillarity, which being heated, boils and burns. (See Rosix-GAS.) Several fat oils, mixed with one or two per cent. of sulphuric acid, assume in stantly a dark green or brown hue, and, when allowed to stand quietly, deposit a coloring matter after some time. It consists in a chemical combination of the sulphuric acid, with a body thus separat ed from the oil, which becomes in con sequence more limpid, and burns with a brighter flame, especially after it is wash ed with steam, and clarified by repose or filtration. Any remaining moisture may be expelled by the heat of a water bath.
The oils combine with the salifiable bases, and give birth to the substance called glycerine, (the sweet_prineiple,)and to the margaric, oleic, and steam acids. The general product of their combination with potash or soda, is Som., which see. Caustic ammonia changes the oils very difficultly and slowly into a soap ; but it readily unites with them into a milky emulsion called volatile liniment, used as a rubefacient in medicine. Upon mix ing water with this liquor, the oil separ ates in an unchanged state. By longer contact, ammonia acts upon oils like the other alkalies. Sea-salt dissolves in small quantity in the oils, and so does verdigris. The latter solution is green. Oils disc solve also several of the vegetable alkalies, as morphia, cinchonia, quinia, strychia, and delphia.
The following is the chemical composi tion of a few of the fixed oils :— De Saussure concludes that the less fusible fats contain more carbon and less oxygen, and that oils are more soluble in alchohol, the more oxygen they contain.
Oil of almonds, according to Gusseron, contains no stearine ; at least he could obtain none by cooling it and squeezing it successively till it all congealed.
Oil of coins is obtained from the seeds of lima-lea eampestris, to the amount of 39 per cent. of their weight. It forms an excellent lamp oil, and is much employed in France.
' The corylus avellana furnishes in oil 60 per cent. of the weight of the nuts.
Rempeeed oil resembles the preceding, but has a disagreeable smell, and a mawkish taste. It is used extensively for making both soft soap and varnishes.
Linseed oil is obtained in greatest puri ty by cold pressure ; but, by a steam heat of about 200° F., a very good oil may be procured in larger quantity. The pro portion of oil usually stated by authors is 22 per cent. of the weight of the seed ; but by hydraulic pressure, from 26 to 27 is obtained. It dissolves in 5 parts of boiling alcohol, in 40 parts of cold alco hol, and in 1.6 parts of ether. When' kept long cool in a cask partly open, it deposits masses of white stearin° along with a brownish powder. That stearine is very difficult of saponifica tion.
Hustard-seed oil. The white or yellow seed affords 36 per cent, of oil, and the black seed 18 per cent. The oil con cretes when cooled a little below 32° F. Nut oil is at first greenish colored, but becomes pale yellow by time. It con geals at the same low temperature as lin seed oil, into a white mass, and has a more drying quality than it.
Oil of olives is sometimes of a greenish, and at others of a pale yellow color. It is prepared from ripe olives, gathered late in autumn. The pulp is separated from the kernels by passing them be tween stones : they are then pressed in rush bags: its specific gravity is 915. A few degrees above 32° F. it begins to de posit some white granules of stearine, especially if the oil have been originally expressed with heat. At 22° it deposits 28 per cent, of its weight in stearine, which is fusible again at 69°, and affords 72 per cent. of oleine. According to Kerwych, oleine of singular beauty may be obtained by mixing 2parts of olive oil with 1 part of caustic soda ley, and ma cerating the mixture for 24 hours with frequent agitation. Weak alcohol must then be poured into it, to dissolve the stearine soap, whereby the oleine, which remains meanwhile unsaponified, is se parated, and floats on the surface of the liquid. This being drawn off, a fresh quantity of spirits is to be poured in, till the separation of all the oleine be com pleted. It has a slightly yellowish tint, which may be removed by means of a little animal charcoal mixed with it in a warm place for 24 hours. By subsequent filtration, the oleine is obtained limpid and colorless, of such quality that it does not thicken with the greatest cold, nor does it affect either iron or copper instru ments immersed in it.