14 HUMAN PHYSIOLOGY. 



The fatty acids thus obtained are characterized by certain chemic features* 

 as follows: 



Stearic acid is a firm, white solid, fusible at 69 C. It is soluble in ether 

 and alcohol, but not in water. 



Palmitic acid occurs in the form of white, glistening scales or needles, 

 melting at 62 C. 



Oleic acid is a clear, colorless liquid, tasteless and odorless when pure. 

 It crystallizes in white needles at o C. 



If this saponification take place in the presence of an alkali e. g., potas- 

 sium hydroxid, sodium hydroxid the acid produced combines at once with 

 the alkali to form a salt known as a soap, while the glycerin remains in solu- 

 tion. The reaction is as follows: 



3 KHO+(C 18 H 84 2 ) 3 = 3 (KC 18 H 33 2 )+3H 2 0. 

 Potassium. Oleic Acid. Potassium Oleate. Water. 



All soaps are, therefore, salts formed by the union of alkalies and fat 

 acids. The sodium soaps are generally hard, while the potassium soaps are 

 soft. Those made with stearin and pahnitin are harder than those made 

 with olein. If the soap is composed of lead, zinc, copper, etc., it is insoluble 

 in water. 



Emulsification. When a neutral oil is vigorously shaken with water or 

 other fluid, it is broken up into minute globules that are more or less per- 

 manently suspended; the permanency depending on the nature of the liquid. 

 The most permanent emulsions are those made with soap solutions. The 

 process of emulsification and the part played by soap, can be readily observed 

 by placing on a few cubic centimeters of a solution of sodium carbonate 

 0.25 per cent, of a small quantity of a perfectly neutral oil to which has been 

 added 2 or 3 per cent, of a fat acid. The combination of the acid and the 

 alkali at once forms a soap. The energy set free by this combination rapidly 

 divides up the oil into extremely minute globules. A spontaneous emulsion 

 is thus formed. 



THE PROTEINS. 



The proteins constitute a group of organic bodies which are found in both 

 vegetable and animal tissues. Though present in all animal tissues, they are 

 especially abundant in muscles and bones, where they constitute twenty 

 per cent, and thirty per cent, respectively. Though genetically related, and 

 possessing many features in common, the different members of the protein 

 group are distinguished by characteristic physical and chemic properties. 



