CETYLIC ACID. 73 



which on the addition of hydrochloric acid we can separate the 

 cetylic acid. 



Tests. When the acid occurs pure and isolated, it is not diffi- 

 cult to distinguish it from other acids ; its crystallisability and its 

 comparatively high boiling point distinguish it from the other acids 

 of this group, and its volatility from the solid fatty acids. On 

 finding it in a body in which it has not been previously recognised, 

 we should always institute an elementary analysis, and determine 

 its saturating capacity, since it is not only possible but very 

 probable that several similar acids remain to be discovered. 



Physiological Relations. 



Occurrence. This acid has hitherto only been found in an 

 animal fat, namely spermaceti, in combination with hydrated oxide 

 of cetyl, and in Japanese wax (Meyer) in combination with oxide 

 of Hpyl. 



Origin. If margaric acid were actually an acid homologous to 

 cetylic acid and to the acids of this group generally, we might easily 

 understand that cetylic acid was produced from this acid in the same 

 manner as acetic is formed from metacetonic acid, for margaric acid 

 stands in the same relation to cetylic acid as metacetonic acid does to 

 acetic acid ; the difference between each pair being C 2 H 2 . 



It is impossible at present to form any conjectures regarding 

 the special importance of these acids in the few positions in which 

 they are principally deposited. For a description of hydrated 

 oxide of cetyl see " haloid bases and fats" 



NON-NITROGENOUS ACIDS. 

 = C a H n _ 2 3 .HO. 



The acids of this group are only interesting in reference to zoo- 

 chemistry inasmuch as, like many acids of the previous group, they 

 are products of decomposition of very common animal matters, and 

 especially of fats. These acids may also be regarded as conjugated 

 oxalic acids, combined with a carbo-hydrogen isomeric with olefiant 

 gas ; at least some of the reasons which have been advanced by 

 Kolbe in support of the theoretical composition of the preceding 

 group, favour this hypothesis. These acids with their empirical 

 and hypothetical formulae are as follows : 



