238 ANIMAL FATS AND PHOSPHATIDES. 



various fatty acids from each other, we must refer to more complete 

 hand-books. 



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

 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 titrat- 

 ing the fat dissolved in alcohol-ether with N/10 alcoholic caustic potash, using 

 phenolphthalein as indicator. 2. The saponification equivalent, which gives 

 the milligrams of caustic potash uniting with the fatty acids in the saponification 

 of 1 gram fat with N/2 alcoholic caustic potash. 3. REICHERT-MEISSL'S equivalent, 

 which gives the quantity of volatile fatty acids contained in a given amount 

 of neutral fat (5 grams). The fat is saponified, then acidified with mineral acid, 

 and distilled, whereby the volatile fatty acids pass over; the distillate is then 

 titrated with alkali. 4. Iodine equivalent is the quantity of iodine absorbed by 

 a certain amount of the fat by addition. It is chiefly a measure of the quantity 

 of unsaturated fatty acids, principally oelic acid or olein, in the fat. Other bodies, 

 such as cholesterin, may also absorb iodine or halogens. The iodine equiva- 

 lent is generally determined according to the method suggested by v. HUBL. 

 5. The acetyl equivalent measures the quantity of those constituents of fats which 

 contain OH groups, and is found by converting these bodies (oxyfatty acids, 

 alcohols and others) into the corresponding acetyl ester by boiling them with 

 acetic acid anhydride. 



In the quantitative estimation of fats, the finely divided dried tissues 

 or the finely divided residue from an evaporated fluid is extracted with 

 ether, alcohol-ether, benzene, or any other proper extraction medium. 

 The lecithin (phosphatides) and other bodies are dissolved by the various 

 extraction media, hence the results for fats are too high. The most 

 exact method for the estimation of fat seems to be the method sug- 

 gested by KTJMAGAWA and SUTO/ who give a complete review of the 

 literature of the subject. 



The fats are poor in oxygen, but rich in carbon and hydrogen. They 

 therefore represent a large amount of chemical energy, and yield correspond- 

 ingly large quantities of heat on combustion. They take first rank 

 among the foods in this regard, and are therefore of very great impor- 

 tance in animal life. We will speak more in detail of this significance, 

 also of fat formation and of the behavior of the fats in the body, in the 

 following chapters. 



Cholesterin and isocholesterin ester, which will be discussed in a sub- 

 sequent chapter, as well as the following bodies, are closely related to 

 the fats. 



Spermaceti. In the living spermaceti or white whale there is found, in a large 

 cavity in the skull, an oily liquid called spermaceti, which on cooling, after death, 

 separates into a solid crystalline part ordinarily called SPERMACETI, and into a 

 liquid, SPERMACETI-OIL. This last is separated by pressure. Spermaceti is also 

 found in other whales and in certain species of dolphin. 



The purified, solid spermaceti, which is called CETIN, is a mixture of esters of 

 fatty acids. The chief constituent is the cetyl-palmitic ester mixed with small 



1 Biochem. Zeitschr., 8. See also y. Schimidzu, ibid., 28. 



