274 LIPOIDS. 



Preparation. In order to obtain hydrated oxide of cetyl, pul- 

 verised hydrated potash must be added to melted spermaceti, and 

 the mixture be continuously stirred ; when the mass has become 

 solid it must be digested with water, and the soap which is thus 

 produced must be treated with hot dilute hydrochloric acid ; after 

 the oily stratum has been again fused with caustic potash, and 

 digested with hydrochloric acid in order to ensure the perfect 

 decomposition of the cetin, the mixture of cetylic acid and oxide of 

 cetyl must be digested with milk of lime and evaporated. From this 

 mixture we can take up the hydrated oxide of cetyl by cold alcohol, 

 which does not dissolve the cetylate of lime. 



Tests. It is impossible to recognise this substance with cer- 

 tainty unless by an elementary analysis. 



Physiological Relations. 



Hydrated oxide of cetyl has not yet been found in an isolated 

 form ; spermaceti, however, occurs in several parts of the Cachalot, 

 mixed with ordinary fat ; in greatest quantity, however, in the head, 

 not in the actual cavity of the cranium, but in a large excavation on 

 either side of the upper part of the head and lying external to the 

 nostrils. Regarding the formation and uses of this substance, 

 we can only offer the same opinions as respecting the fats in 

 general. 



The doeglic oxide of Scharling is too hypothetical a body to 

 be entitled to be yet classed among the haloid bases. Compare 

 p. 11(5. 



LIPOIDS. 



Under this head we place what are termed the non-saponifiable 

 fats, that is to say, such bodies as have many physical properties 

 in common with the salts of oxide of lipyl, but do not resemble 

 them in their composition or in their products of decomposition, and 

 consequently cannot be placed amongst the true fats. In this class 

 we place cholesterin, serolin, casiorin, and ambrein. 



