FATS, WAXES, AND LIPOIDS 149 



Coconut oil, from the seeds of the coconut, is commonly called 

 copra oil. Copra soaps can absorb large quantities of salt solu- 

 tion and are hence in demand for washing with sea water. Palm 

 oil, which comes from one of the African palms, has the consist- 

 ency of lard and turns yellow when exposed to the air. It is used 

 in soaps and also has been used in margarines for food, but this 

 is now illegal in the United States. 



Cottonseed oil, which is extracted from the seed of cotton, is 

 used in foods as a substitute for olive oils or when hydrogenated 

 for lard. It is also used in the manufacture of soap and certain 

 rubber substitutes. 



Linseed oil, from the seed of flax, is used chiefly in the manu- 

 facture of paints, varnishes, and printer's ink because of its rapid 

 drying qualities. Other oils, such as walnut and poppy oil, are 

 used especially for the paints of artists. 



Olive oil, which is extracted from the fruit of the olive, is used 

 largely in southern Europe for cooking. Poorer grades of oil are 

 used in the soap industry. 



General Characters. — The fats are all lighter than water and 

 are insoluble in it. They dissolve readily, however, in ether, 

 chloroform, and carbon disulphide. They may be saponified, as 

 described below, and they leave a permanent translucent stain 

 on paper. 



They are all esters of the trihydric alcohol, glycerol. In the 

 chapter on the chemistry of chlorophyll it was pointed out that 

 an ester is a "salt" of an alcohol and an acid. Just as sodium 

 chloride is formed by the union of sodium hydroxide (NaOH) 

 and hydrochloric acid (HC1) with the release of water: 



NaOH+HCl = NaCl+H 2 



so, e. g., ethyl alcohol may combine with formic acid to form the 

 ester, ethyl formate, and water: 



C 2 H 5 OH+HCOOH = C 2 H 5 COOH+H 2 0. 



This general reaction between an acid and an alcohol may be 

 represented thus : 



R.OH+H.OOCR=R.OOCR+H 2 0. 



