OILS AND FATS. 83 



m water, but slightly soluble in alcohol, with the exception of castor 

 oil, but soluble in ether and in volatile oils. 



Although oils appear to be homogeneous, they in reality consist 

 of several proximate principles. Of these, the most solid one in 

 animal oils is called steariii; in vegetable oils, margarin; the most 

 liquid in both is named olein^ or elain. These principles may easily 

 be isolated by submitting the whole to boiling alcohol, which, on 

 cooling, deposites the margarine and stearine, but retains the olein. 

 The margarine may be then separated from the stearine by etherj 

 and the olein from the alcohol by distillation. These three principles 

 consist respectively of an acid, united with a base. The acid is 

 named oleic, stearic, and margaric; the base is the same for each ; 

 it is called glycerine. 



When any of the fixed oils or fats are mixed with an alkali, a 

 change takes place denominated saponification, resulting in the for- 

 mation of a soa'p; the several acids just mentioned quit the gly- 

 cerine with which they were united, and combine with the alkali. 

 Thus common soap, made by the action of potassa on fat, consists 

 chiefly of a stearate of potassa. If a soap be decomposed by an 

 acid, the particular fat acid of which the soap may have been con- 

 stituted will be precipitated. The formation of the lead plaster is a 

 true instance of saponification, the oleo-margarate of lead being 

 formed, and the glycerine remaining in solution. 



Spermaceti. — This substance is found in the cranium of a certain 

 species of whale, in union with an oil. It has a crystalline struc- 

 ture, melts at 120°, is soluble to some extent in boiling alcohol, also 

 in ether. It is saponified with difficulty, two substances resulting, 

 called ethal and ethalic acid. 



Wax.— Th:\s substance, whether procured from the bee, or from 

 the pollen and leaves of flowers, is found to consist of two distinct 

 principles termed ceri7ie and myricine; these principles may be 

 separated by boiling alcohol. 



All the fixed oils are compounds of carbon, oxygen, and hydrogen. 



Volatik Oils. — These are very numerous, and impart the peculiar 

 odours to plants. They are procured from the various parts of plants 

 by distillation with water, common salt being sometimes added to 

 elevate the boiling point. 



When pure, they are colourless, but they generally have a slight 

 tinge ; they have a powerful odour and strong taste ; do not sapo- 

 nify; absorb oxygen when exposed to the air; are freely miscifele 

 with the fixed oils ; are very slightly soluble in water ; freely so in 

 alcohol and ether. They consist of two , proximate principles, ana- 

 logous to those of the fixed oils, and named stearoptln and eleaoptin. 



Some of the volatile oils, consist solely of carbon and hydrogenj 

 as the oil of turpentine ; others, of carbon, hydrogen, and oxygen ; 

 and a few contain sulphur, as the oils of mustard, horseradish, &c' 



