LIPIDES 83 



c)i spliiting of fats into their constituent parts may be accomplished 

 by various means. For example, fats hydrolyze very slowly when 

 intimately mixed with water. On the other hand, hydrolysis becomes 

 fairly rapid when a fat is treated with steam. The rate of hydrolysis 

 is increased even more if an emulsifying agent is added, thereby 

 increasing the contact between the fat and water surfaces. An example 

 of such an emulsifier is Twitchell's reagent, which consists of naph- 

 thalene, oleic acid, and sulfuric acid. When a fat that has been pre- 

 heated with steam comes into contact with small quantities of Twitch- 

 ell's reagent, and the mixture is heated to the boiling point, hydrolysis 

 occurs in a very short time. 



When fats are intimately mixed with an alcoholic solution of a 

 strong alkali, such as sodium or potassium hydroxide, and are heated, 

 the glyceride molecules are split, yielding glycerol and the sodium or 

 potassium salts of the fatty acids. This process is called saponification 

 (soap producing), and the metallic salts of the fatty acids are called 

 soaps. The saponification reaction may be represented as follows: 



CHo— OOC(CH.)i6CH3 CH2OH 



1 ' 1 



CH— OOC(CH.)i6CH3 -f 3NaOH -^ CHOH -f 3CH3(CHo)i6COONa 



I I 



CH2— OOC(CH2)i6GH3 CH2OH 



tristearin glycerol sodium stearate 



(a soap) 



Soaps may be divided into two classes, hard soaps and soft soaps. 

 Hard soaps, such as the common bar soaps, are the sodium salts of 

 the higher fatty acids. Soft soaps are the potassium salts of the higher 

 fatty acids and are usually marketed as semiliquids or pastes. The 

 fatty acid salts of magnesium and calcium and the heavy metals, such 

 as lead and zinc, are insoluble in water. When a sodium or potassium 

 soap is added to "hard" water (water containing calcium or magne- 

 sium salts in solution), the sodium or potassium atom is replaced by 

 calcium or magnesium, forming a soap insoluble in water: 



2CH3(CH2)i6COONa -f Ca(HC03)2 -^ 



soluble calcium 



sodium soap bicarbonate 



[CH3(CH2)i6COO]2Ca + 2NaHC03 



insoluble sodium 



calcium soap bicarbonate 



The formation of such insoluble soaps explains the presence of "curds" 

 when ordinary soaps are used in hard water. 



Calcium soaps are employed industrially as lubricating greases. 

 Zinc soaps, especially zinc stearate, are used extensively in talcum 



