LIPIDES 87 



I g. of the fat will be relatively few, and the saponification number 

 will be low. On the other hand, the saponification number will be 

 high if there is a predominance of shorter-chain fatty acids combined 

 with the glycerol in a fat. It can be stated, therefore, that the saponi- 

 fication number varies inversely with the mean molecular weight of 

 the fatty acids bound as glycerides. 



The degree of unsaturation of a fat may be determined by allowing 

 a known amount of fat to react with solutions of known strength con- 

 taining iodine chloride (Wijs solution) or iodine bromide (Hanus 

 solution). The iodine adds to the double bonds of the unsaturated 

 fatty acid portion of the glyceride molecules, each double bond absorb- 

 ing 2 atoms of iodine. The iodine number is defined as the number 

 of grams of iodine absorbed by 100 g. of a fat. Although the iodine 

 number indicates the total amount of unsaturation in a fat, it gives 

 no indication of the number of double bonds in any particular fatty 

 acid or glyceride. 



An index of the amount of volatile fatty acids in the glycerides of 

 a fat can be ascertained by means of the Reichert-Meissl number. 

 A known weight of fat is saponified, the soaps are converted to free 

 fatty acids, and these are subjected to distillation with live steam. 

 Those acids containing from 4 to 10 carbons are quite volatile with 

 steam and are removed by distillation and titrated with O.LV KOH. 

 The number of milliliters of O.IN KOH required to neutralize the 

 volatile, soluble fatty acids from 5 g. of a fat is called the Reichert- 

 Meissl number. Butterfat is an exception to the rule which states that 

 naturally occurring fats contain relatively small amoimts of volatile 

 fatty acids. Whereas the Reichert-Meissl numbers of coconut oil and 

 palm oil range between 5 and 8, the value for butterfat ranges from 

 21 to 33. The high Reichert-Meissl number of butterfat makes it 

 possible to detect the presence of foreign fats which are sometimes 

 used as adulterants in the manufacture of butter. 



PHOSPHOLIPIDES 



From a biological standpoint, the phospholipides are one of the 

 most important classes of lipides. Although found in most plant and 

 animal tissues, they are particidarly abundant in such active organs 

 as the liver and the brain. The best-known members of the phos- 

 pholipide group are the lecithins, the cephalins, and the sphingo- 

 myelins. 



Lecithins and cephalins are soluble in ether and are extracted from 



