266 PHYSIOLOGICAL CHEMISTRY 



it will rise to the surface. This layer containing much fat is 

 known as cream. 



8. Saponification of Fats. If a fat is heated with an alkali 

 it is split into fatty acids and glycerine. The liberated fatty 

 acids unite with any excess of alkali to form soaps, hence the 

 term saponification. 



In a flask heat to boiling on the steam bath 50 c.c. of alcoholic 

 sodium hydrate and add 5 c.c. of olive or cottonseed oil and con- 

 tinue heating. The saponification is complete when all the oil 

 has disappeared. This may occur almost immediately. When 

 this point has been reached, transfer to an evaporating dish, add 

 about 75 c.c. of water and heat on the water bath to drive off 

 the alcohol. When the alcohol has been removed (decide this by 

 the odor) divide the liquid into three parts. Filter if necessary. 

 To one portion add dilute sulphuric acid and warm on the water 

 bath. The acid converts the soaps into free fatty acids which 

 form an oily layer at the surface (oleic acid). If a palmitic or 

 stearic acid fat is used, the fatty acids separate in solid form. 



To a second portion of the sodium soap solution add an equal 

 volume of saturated sodium chloride. The soap is "salted out" 

 since it is insoluble in sodium chloride solution. In case no pre- 

 cipitate forms evaporate the solution on the water bath to a 

 smaller volume. 



To the third portion of the sodium soap solution add calcium 

 chloride solution. The precipitate is calcium soap, which is 

 more insoluble than sodium soap. Hard water, which contains 

 calcium salts, is unsuitable for washing purposes, for the cal- 

 cium precipitates soap in white flakes, and thus removes it 

 from solution. 



9. Acrolein Test. If a fat is heated with boric acid or potas- 

 sium bisulphate, acrolein is formed, which may be recognized by 

 its sharp, disagreeable odor. Heat a small amount of lard or 

 olive oil with boric acid or potassium bisulphate in a dry test 

 tube. Continue the heating until the material has become prac- 

 tically dry and note the penetrating odor of acrolein. Eepeat 

 the test using a few drops of glycerine in place of the lard. 



