OIL. 



are also obtained from animals ; such as 

 train oil, as it is called, which is extract- 

 ed from the fat or blubber of the whale. 

 Fixed oil is obtained also in great abun- 

 dance from the liver of animals, and is 

 found to exist in the eggs of fowls. These 

 different kinds of fixed oils, although they 

 possess many common properties, yet in 

 others they are very different. Many cf 

 the vegetable oils have no smell, aiici 

 scarcely any perceptible taste. The 

 animal oils, on the contrary, are generally 

 extremely nauseous and offensive. These 

 differences are supposed to be owing to 

 the mixture of extraneous bodies, or to 

 certain chemical changes which arise 

 from the action of these bodies upon each 

 other, or on the oil itself. As the fixed 

 oils exist ready formed in the seeds of 

 plants, they are generally obtained by 

 " expression," and hence they have been 

 called " expressed oils." This is done 

 by reducing the seeds to a kind of pulp, 

 or paste, which is enclosed in bags, and 

 subjected by means of machinery, when 

 it is obtained in the large way, to strong 

 pressure, so that the oil flows out, and 

 is easily collected. The oil which is 

 obtained by this process, which has 

 been called " cold drawn oil," be- 

 cause it is procured without the ap- 

 plication of heat, and merely by pressure, 

 is the purest; but the quantity which 

 seeds in general yield is comparatively 

 small, and some seeds which contain a 

 considerable portion of oil scarcely afford 

 any when treated in this way. It there- 

 fore becomes necessary for extracting the 

 oil from seeds of the latter description, 

 and to have it in greater abundance from 

 all seeds, to employ heat to facilitate the 

 separation of the oil from the mucilage, 

 or other matters with which it is com- 

 bined. For this purpose heat is applied, 

 either to the apparatus which is employ- 

 ed in pressing out the oil, or the bruised 

 seeds are exposed to the vapour of water, 

 and sometimes they are boiled in the wa- 

 ter itself; by which means those sub- 

 stances which are soluble in water are 

 separated, and thus the oily part which 

 adhered to these substances is disen- 

 gaged. The oils which are obtained in 

 this manner are very impure. They are 

 mixed with mucilage, and other parts of 

 the substances from which they have 

 been extracted. Many of these matters 

 separate from the oils when they are left 

 at rest. They are sometimes mechanical- 

 ly purified by filtration through coarse 

 cloths, by which means the grosser parts 

 are separated. Different oils too, it is 

 said, undergo different kinds of purifica- 



tion by different manufacturers, but these 

 processes are kept secret. After they 

 have remained at rest for some time, they 

 are filtered and agitated with water, by 

 which the parts that are soluble in this 

 fluid are separated from the oil. Some- 

 times they are gently heated, for a short- 

 er or longer time, according to the na- 

 ture of the substances with which the oil 

 is contaminated. Acids diluted with wa- 

 ter are employed to separate the muci- 

 lage ; lime and the alkalies are also used 

 to combine with an acid which holds this 

 mucilage in solution, and thus to favour 

 its precipitation. Alum, chalk, clay, and 

 ashes, are also employed in the purifica- 

 tion of oils. 



Fixed oils are generally liquid, but of a 

 thick, viscid consistence, and in general 

 they are lighter than water. The speci- 

 fic gravity varies from 0.91, which is that 

 of olive oil, to 0.94, that of linseed oil, 

 The boiling point of the fixed oils is not 

 under the temperature of 600. When 

 exposed to cold they congeal, and even 

 crystalize. There is, however, a con- 

 siderable variety in this respect among 

 fixed oils : some become solid at the tem- 

 perature of a few degrees above the 

 freezing point of water ; while others, on 

 the contrary, require a degree of cold 

 = 5 ; and some remain fluid when ex- 

 posed to the greatest cold. Those oils, 

 it has been observed, which most readily 

 become solid, such as olive oil, are least 

 subject to change ; while those which 

 congeal with difficulty have a greater 

 tendency to spoil and become rancid. 

 When fixed oil is exposed to heat it does 

 not evaporate, till it is raised to the tem- 

 perature of boiling, or 600 ; but when it 

 is thus raised in vapour its properties are 

 changed. It is decomposed by the sepa- 

 ration of some of its principles. The part 

 that is volatilized has a greater proportion 

 of hydrogen ; charcoal is deposited, and 

 water and sebacic acid are formed, while 

 carbonated hydrogen gas is disengaged. 

 When oil is exposed to the open air, and 

 a burning body is brought in contact with 

 it, it readily takes fire, and burns rapidly, 

 with a yellowish white flame. It is on 

 this conversion of oil into vapour, and the 

 inflammation of this vapour, that the ap- 

 plication of oil in lamps and candles de- 

 pends. The oil is gradually and in small 

 quantities brought in contact with the 

 burning part of the wick ; it is converted* 

 into vapour, which is immediately in- 

 flamed, and continues to burn till new 

 portions are supplied, to undergo the 

 same change, and thus keep up a constant, 

 and uniform light and heat. According 



