52 FATS, OILS, AND WAXES 



animal tissues, adds considerably to the difficulty of their 

 preparation in a pure condition ; moreover, a given lipin 

 which may be extracted by means of ether in admixture with 

 another lipin may, in a purified condition, be practically in- 

 soluble in this solvent. 



Again, it was first found by Hoppe Seyler * that when egg 

 yolk is extracted with ether until no more extract is obtained, 

 the residue still contains lipins which can be readily extracted 

 by means of warm alcohol ; this has since been found to be a 

 property common to all tissues both plant and animal ; no 

 matter how long the extraction with ether is continued, a 

 considerable quantity of the lipin is retained by the tissue 

 only to be extracted by replacing the ether by alcohol. 



In general, the first step in the purification of an ether 

 extract from lipin consists in the addition to the concentrated 

 ethereal solution of four times its volume of cold acetone, which 

 will precipitate the phospholipins and probably also the 

 cerebrosides if present. The separation of fat from lipin by 

 this method will only be partial, and repeated solution and 

 precipitation will be required to effect any reasonable amount 

 of purification, f 



In order to distinguish a Hpin from a fat, recourse is taken 

 to the fact that the former, unlike fats, contain either nitrogen 

 or phosphorus or both. To establish the presence of nitrogen, 

 it is sufficient to heat the purified substance with a little soda 

 lime and to test for the evolution of ammonia by red litmus 

 paper. Phosphorus may be detected by fusing with fusion 

 mixture on a platinum foil until all carbon is burnt away, 

 the residue is dissolved in nitric acid and tested for the presence 



* Hoppe Seyler ; " Med. chem. Unters.," 1869, 3, 392. 



t On applying this method to the ether-soluble extract of cabbage-leaf 

 cytoplasm, Chibnall and Channon (" Biochem. Journ.," 1927, 21, 233) claim 

 to have precipitated, not an ordinary phospholipin, but the calcium salt 

 of a diglyceride phosphoric acid, to which they assign the formula — 



CH2O— CORi 



i 



HO— COR2 



CHp— P^O 



0>Ca 



