228 PHYSIOLOGICAL CHEMISTRY 



above, shaking after each, addition until after a vigorous shaking 

 the pink color in the alcohol layer just remains. Allow the two 

 layers to separate in a large test tube. Draw off by means of a 

 pipette the layer of neutral oil, wash it by shaking gently with 

 one or two portions of distilled water in a test tube, and save it 

 for use in the experiments following where neutral oil is called 

 for. 



v. Emulsification. The property of forming an emulsion is 

 of great importance. The fat is held in suspension in the liquid 

 in the form of minute droplets. Study the conditions affecting 

 emulsification as follows : 



(a) Shake together thoroughly about 1 c.c. of neutral oil and 

 a few c.c. of water. The oil and water quickly separate into two 

 layers. 



(b) Repeat (a), first adding a small amount of sodium car- 

 bonate solution to the tube. The milky appearance of the water 

 layer indicates that a portion of the oil has emulsified, but the 

 action is not extensive. To neutral oil and water add soap solu- 

 tion and shake. A good emulsion forms, indicating the favorable 

 action of soap on emulsion formation. Upon this property of 

 soap depends in large measure its usefulness in cleansing. Greasy 

 material on the surface washed is emulsified, and the insoluble 

 ''dirt" thus liberated and carried away by the water and the 

 "suds." 



If rancid oil (oil which contains free fatty acid), water and an 

 alkali, e.g. Na 2 C0 3 are shaken together a good emulsion is formed, 

 since the mixture contains the soap produced by the action of the 

 fatty acids and the alkali. 



(c) To neutral oil and water add albumin solution and shake 

 thoroughly. Albumin is a good emulsifying agent. 



(d) To neutral oil and water add gum arabic (acacia) solu- 

 tion and shake. Gum arabic also is a good emulsifier. 



(e) Lymph has the power of aiding in the formation of an 

 emulsion. This may be demonstrated (Ranvier's experiment) 

 by bringing drops of oil and lymph together under the micro- 



