112 OILY FATTY ACIDS. 



OILY FATTY ACIDS. 



This group of bodies contains a far smaller number of members 

 than the preceding groups. At present the following are the only 

 oily fatty acids with which we are acquainted : 



Oleic acid ................ C 



Erusicacid 

 Doeglicacid 



Erusicacid ................ C 44 H 41 O 3 .H(X 



Ricinoleic acid, containing the same group of atoms of carbon 

 and hydrogen with 5 atoms of oxygen (=C 38 H 35 O 5 .HO), bears 

 the same ratio to the last of these acids, which salicylous acid bears 

 to benzoic acid. 



Dissimilar as, on the whole, is the composition of the oily and 

 the solid fatty acids, they are yet similar in most of their physical 

 and even in many of their chemical properties. 



Whether campholic acid C 20 H 17 O 3 .HO, and the two isomeric 

 acids, campheric acid and angelic adc?=zC 10 H 7 O 3 .HO, belong to 

 this group (for their composition accords with the general formula 

 C m H m _ 3 O 3 .HO) is as yet undecided ; several of their physical 

 properties (for instance., they are solid, crystallisable, and volatile,) 

 do not accord with this view, but these acids may possibly bear the 

 same relation to the oily acids, that the acids of the first group 

 bear to the solid fatty acids, and the low atomic weight of the 

 radical may also be the cause of this difference in their properties. 



OLEIC ACID. C 36 H 33 O 3 .HO. 



Chemical Relations. 



Properties. This body, known also as elaic acid, is, when 

 perfectly pure, and at a temperature above + 14, of an oily con- 

 sistence, limpid, devoid of colour, taste, and smell, and exerts no 

 action on litmus ; at + 4 it forms a white, crystalline mass, which, 

 at the moment when it solidifies, strongly contracts and expresses the 

 still oily portion ; it is then very hard, and is unaffected by ex- 

 posure to the atmosphere ; on exposing an alcoholic solution to 

 extreme cold it crystallises in long needles. In its fluid condition, 

 that is to say, as oil, it rapidly absorbs oxygen and becomes changed. 

 When heated, it becomes decomposed, yielding not only carbon 





