246 PHYSIOLOGICAL CHEMISTRY. 



Oleic acid forms at ordinary temperature a colorless, tasteless, 

 and odorless oily liquid which crystallizes at about + 4 C. On 

 being heated it yields, besides volatile fatty acids, SEBACIC ACID, 

 C 10 H 18 0, which crystallizes in shining plates and melts at -J- 127 C. 

 Oleic acid is converted by nitrous acid into its isomer, ELAIDIC ACID, 

 which is a solid, melting at +45 C. Oleic acid is insoluble in 

 water but dissolves in alcohol, ether, and chloroform. With con- 

 centrated sulphuric acid and some cane-sugar it gives a beautiful 

 red or red dish- violet liquid whose color is similar to that produced 

 in PETTENKOFER'S test for bile-acids. 



If the watery solution of the alkali combinations of oleic acid is 

 precipitated with lead acetate, a white, tough, sticky mass of oleate 

 of lead is obtained which is not soluble in water and only slightly 

 in alcohol, but is soluble in ether (differing from the lead-salts of 

 the other two fatty acids). 



An acid related to oleic acid, DOGLINGIC ACID, which is solid at C., liquid 

 at -\- 16, and soluble in alcohol, is found in the blubber of the BAL^ENA 



ROSTRATA. 



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

 fat must first be extracted with ether. After the evaporation of the 

 ether the residue is tested for fat and the acrolein test must not be 

 neglected. If this test gives positive results, then neutral fats are 

 present; if the results are negative, then only fatty acids are present. 

 If the above residue after evaporation gives the acrolein test, then a 

 small portion is dissolved in alcohol-ether free from acid and which 

 has been colored bluish violet by tincture of alkanet. If the color 

 becomes red, a mixture of neutral fat and fatty acids is present. In 

 this case the fat is treated in the warmth with a soda solution and 

 evaporated on the water-bath, constantly stirring until all the water 

 is removed The fatty acids are hereby combined with the alkali 

 as soaps, while the neutral fats are not saponified under these con- 

 ditions. If this mixture of soaps and neutral fats is treated with 

 water and then shaken with pure ether, the neutral fats are dis- 

 solved, while the soaps remain in the watery solution. The fatty 

 acids may be separated from this solution by the addition of a 

 mineral acid which sets the acid free. 



The neutral fats separated from the soaps by means of ether are 

 contaminated with some cholesterin, which must be separated in 

 quantitative determinations by saponification with alcoholic caustic 

 potash. 



The cholesterin is not attacked by the caustic alkali while the 

 neutral fats are saponified. After the evaporation of the alcohol 



