432 OILS 



escitlenta, contains a fat oil. The quantity of oil furnished by seeds varies not only 

 with the species, but, in the same seed, with culture and climate. Nuts contain 

 about half their weight of oil ; the seeds of the Brassica oleracea and B. campcstris, 

 one-third ; the variety called colza in France, two-fifths ; hemp-seed, one-fourth ; and 

 linseed from one-fourth to one-fifth. Unverdorben states that a last, of 10 quarters, 

 of linseed, yields 40 ahms = 120 gallons English, of oil ; which is about 1 cwt. of oil 

 per quarter. 



The fat oils, when first expressed without much heat, taste merely unctuous on tho 

 tongue, and exhale the odour of their respective plants. They appear quite neutral 

 by litmus-paper. Their fluidity is very various, some being solid at ordinary tem- 

 peratures, and others remaining fluid at the freezing-point of water. Linseed-oil, 

 indeed, does not congeal till cooled from 4 to 18 below Fahr. The same kind of 

 seed usually affords oils of different degrees of fusibility ; so that in the progress of 

 refrigeration one portion concretes before another. Chevreul considered all the oils to 

 be composed of two, and sometimes three, different species, viz. stearine, margarine, 

 and oleine ; the consistence of the oil or fat varying as either of these predominates. 

 These bodies are all compounds of glycerine, with a fatty acid. At all ordinary tem- 

 peratures oleiue is liquid ; margarine is solid, and melts at 116 Fahr. ; stearine is still 

 more solid, and melts at about 130 Fahr. The two latter may be prepared from pure 

 mutton fat, by melting it in a glass flask, and then shaking it with several times its 

 weight of ether; when allowed to cool, the stearine crystallises out, leaving the 

 margarine and oleine in solution. The soft mass of stearine may be strongly pressed 

 in a cloth, and further purified by re-crystallisation from ether. It forms a white 

 friable mass, insoluble in water, and nearly so in cold alcohol ; biit boiling spirit 

 takes up a small quantity. It is freely soluble in boiling ether; but, as it cools, 

 nearly all crystallises out. 



Margarine may be prepared from the ethereal mother-liquor, from which the 

 stearine has separated, by evaporating it to dryness ; the soft mixture of margarine 

 and oleine is then pressed between folds of blotting-paper ; the residue again dissolved 

 in ether, from which the margarine may now be obtained tolerably pure. It very 

 much resembles stearine, but, as above mentioned, has a lower melting-point. 



It is rather doubtful if oleine has ever been prepared in a perfectly pure state, the 

 separation of the last particles of margarine being very difficult. It may be obtained 

 by subjecting olive-oil to a freezing mixture, when the margarine will nearly all 

 separate, and the supernatant fluid oil may be taken as oleine. 



Oleine may also be procured by digesting the oils with a quantity of caustic soda, 

 equal to one half of what is requisite to saponify the whole ; the stearine and marga- 

 rine are first transformed into soap, then a portion of the oleine undergoes the same 

 change, but a great part of it remains in a nearly pure state. This process succeeds 

 only with recently-expressed or very fresh oils. 



The fat oils are completely insoluble in water. When agitated with it, the mixture 

 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. Castor oil is the only one which dissolves in 

 cold alcohol. Ether, 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 dis- 

 tillation. 



Fat oils may be exposed to a high temperature without undergoing much altera- 

 tion ; but when they are raised to nearly their boiling-point, they begin to be decom- 

 posed. The vapours that then rise are not the oil itself, but certain products generated 

 in it by heat. These changes begin somewhere under 600 of Fahr., and require for 

 their continuance temperatures always increasing. 



If, instead of raising the heat generally, we submit the fats or oils directly to a red 

 heat, as by passing them through a red-hot tube, they are decomposed completely, and 

 are almost entirely transformed into gaseous carburetted hydrogens, the mixture of 

 which serves for illuminating purposes, and yields a far better light than ordinary 

 coal-gas. In places whore the seed and fish oils can be procured at a low price, these 

 substances might be employed with great advantage for this purpose. 



Action of Alkalis on the Oils. When the fat or oils are boiled with potash or soda, 

 they are decomposed into glycerine and the fatty acids, with assimilation of water by 

 both the glycerine and the fatty acids. Thus oleino yields glycerine and oleic acid ; 

 margarine, glycerine and margaric acid; and stearine, glycerine and stearic acid. 

 Tho glycerine dissolves in the water and the fatty acids unite with the alkalis, 

 forming soaps (see SOAPS). The action of ammonia on the oils is much less energetic ; 

 it, however, readily mixes with them, forming a milky emulsion, called volatile lini- 

 ment, used as a rubefacient in medicine. Upon mixing water with this, or by neutra- 

 lising the ammonia by an acid, or even by mere exposure to the air, the ammonia is 



