230 ANIMAL FATS AND PHOSPHATIDES. 



latter melt at 14 C. Oleic acid is insoluble in water, but dissolves 

 in alcohol, ether, chloroform and petroleum ether. With concentrated 

 sulphuric acid and some cane-sugar it gives a beautiful red or reddish- 

 violet liquid whose color is similar to that produced in PETTENKOFER'S 

 test for bile-acids. If a solution of oleic acid in glacial acetic acid is treated 

 with a little chromic acid (in glacial acetic acid) and then with concentrated 

 sulphuric acid, the green solution gradually becomes violet or cherry- 

 red, and shows two characteristic absorption bands in the green, one a 

 broad band near the blue and a second but fainter band near the yellow 

 (LiFSCHUTz). 1 The barium salt of oleic acid contains 19.65 per cent 

 barium and the silver salt 27.73 per cent silver. 



If the watery solution of the alkali compounds of oleic acid is pre- 

 cipitated with lead acetate, a white, tough, sticky mass of lead oleate is 

 obtained, which is not soluble in water and only slightly in alcohol, but is 

 soluble in ether. This salt is more easily soluble in benzene than the lead 

 salts of stearic and palmitic acids, and this behavior of the lead salts toward 

 ether and benzene is made use of in separating oleic acid from the other 

 fatty acids. 



An acid related to oleic acid, DOEGLIC ACID, which is solid at 4 C., liquid air 

 16 C., and soluble in alcohol, is found in the blubber of the Baloena rostrata. 

 According to BULL this acid is probably only a mixture of oleic acid and another 

 acid gadoleic acid, C 2 oH 38 O 2 , having a melting-point of +24.5 C., and occurring 

 in cod-liver oil, herring oil and in whale blubber. In addition to this acid BULL 

 found in cod-liver oil, besides myristic, palmitic, oleic and erucic acids, another 

 acid, having the formula C 16 H 30 O2. KURBATOFF 2 has demonstrated the presence 

 of linoleic acid in the fat of the silurus, sturgeon, seal, and certain other animals. 

 Drying fats have also been found by AMTHOR and ZINK 3 in hares, wild rabbits, 

 wild boar, and mountain-cock. 



To detect the presence of fat in an animal fluid or tissue the fat must 

 first be shaken out or extracted with ether. After the evaporation 

 of the ether the residue is tested for fat and fatty acids. The neutral 

 fats are differentiated from the fatty acids by the acrolein test, and the 

 fatty acids by the fact that their solution in a mixture of alcohol and ether 

 previously made bluish-violet with tincture of alkanet, becomes red in 

 color. In separating the fats from cholesterin and other non-saponifiable 

 substances, as well as for the determination of the kind of the various 

 fatty bodies, they are saponified with caustic alkali, alcoholic potash, 

 or with sodium alcoholate. In regard to these operations, as well as the 

 further investigation and the separation of the various fatty acids from 

 each other, we must refer to completer hand-books. 



In addition to the methods already suggested there are other chemical meth- 

 ods which are important in investigating fats. Besides ascertaining the melting- 

 and congealing-point we also determine the following: 1. The acid equivalent, 

 which is a measure of the amount of fatty acids in a fat, is determined by 



1 Zeitschr. f. physiol. Chem., 56. 



2 Bull, Ber. d. d. chem. Gesellsch., 39; Kurbatoff, Maly's Jahresb., 22. 



3 Zeitschr. f. anal. Chem., 36. 



