4 SOAPS AND PROTEINS 



in the fat or oil to form the corresponding soaps, while alcohol 

 (glycerin i- >plit off. Expressed graphically and for a single 

 "fat": 



f-O - Ci8H 35 O+3NaOH = 3NaO 



Glyceryl stearate + sodium = sodium stearate + glycerin 



hydroxid 



It is important for our purposes to note, first, the variables 

 contained in the" elements constituting the reaction mixture. 



There is (1) the fat. While all the fats are esters, they run 

 the gamut in mere physical attributes from the extreme, on the 

 one hand, of liquids not unlike water, through viscid oils, to the 

 extreme, on the other hand, of solids like " waxes," which can 

 hardly be broken with a hammer. But, from a chemical point 

 of view, it is obvious that these may also differ widely from each 

 other both as to (a) kind of fatty acid found in the ester, and 

 (6) kind of alcohol united to the fatty acid. Even without 

 embracing the theoretical extremes we find at the one end fatty 

 acids with, say, six carbon atoms in the molecule, while at the 

 other may be those with two dozen. The alcohol found in the 

 fat is usually glycerin, but diatomic or monatomic alcohols may 

 take its place. 



A second variable concerns (2) the hydroxid employed. Since 

 the commoner soaps of commerce are sodium soaps, sodium 

 hydroxid is the alkali ordinarily employed. In " soft " soap 

 manufacture potassium hydroxid is used, for the soft soaps are 

 potassium soaps. Directly or indirectly, however, other hydroxids 

 or bases are of much scientific or technologic importance. Sodium, 

 potassium and ammonium tire of significance when ordinary 

 " washing " soaps are under consideration, but the wide distri- 

 bution ofjnagnesium and calcium compounds in various " waters " 

 makes necessary a knowledge of the properties of the soaps of 

 these metals when " hard " waters are used. The importance 

 of the heavy metals, like zinc and lead, becomes apparent when 

 it is recalled that zinc stearate is used as a dusting powder in 

 skin affections and that the plastic properties of lead plasters 

 and of various paints is dependent upon the lead soaps found or 

 formed in these mixtures. 



