12 LABORATORY WORK IN PHYSIOLOGICAL CHEMISTRY. 



FATTY ACIDS AND SOAPS. 



Since the character of the fatty acid determines the 

 character of the fat, the properties and solubilities of the 

 fatty acids and fats must be similar, as the tests will 

 prove. 



The soaps are salts of the fatty acids; the sodium salts 

 being solid and hard, while those of potassium are soft. 

 Both are soluble in water. The remaining metallic salts 

 are insoluble in water, but generally dissolve in alcohol. 

 The lead combination with oleic acid (lead plaster) differs 

 from the corresponding one with palmitic and stearic acids 

 in being soluble in ether. 



Perform the following reactions with the fatty (oleic) acid: 



(a) Test its solubility in ether; chloroform; water; 

 alcohol. 



(6) Warm some in a dry test-tube with potassium bisul- 

 phate. 



(c) Shake up a few pieces of the fatty acid with 25 c.c. 

 water and add NaOH, drop by drop, until the acid is all dis- 

 solved. Write the reaction. What is formed? 



Use this soap solution for the following reactions: 



(a) Add 5 drops to a saturated solution of NaCl. 



(6) To 5 c.c. of lead acetate add a few c.c. of the soap 

 solution. A sticky precipitate results (lead oleate), which is 

 soluble in ether. Write the reaction. What is the impor- 

 tance of this compound? 



(c) To 50 c.c. of tap water in a flask add the soap solu- 

 tion, drop by drop, alternately shaking until a permanent 

 lather is obtained. The amount of soap solution required 

 to obtain the lather is in direct proportion to the hardness of 

 the water. Explain the chemistry of this experiment. 



