LIPIDES (fats and RELATED SUBSTANCES) 89 



Table 4-6 



Iodine niiinber of some ronimon oils and fats 



Coconut oil 5-10 



Buttcrfat 26-38 



Beef tallow 35-45 



OIoo oil from beef tallow 40- 55 



Lard 50-70 



Olive oil 79-90 



Peanut oil 87-100 



Cottonseed oil 104-1 16 



Corn oil 111-124 



Soybean oil 137-143 



Linseed oil 170-200 



Linseed oil has the highest iodine number of any known fat. It is a 

 highly unsaturated oil and takes up atmospheric oxygen very readily 

 to form a hard tough film. For this reason it is peculiarly well adapted 

 for paint purposes. When paint is spread over a surface, the linseed 

 oil takes up oxygen from the air and forms a thin, hard, watertight coat. 

 No other oil has ever been found which is equal to linseed oil in this 

 respect. Tung and soybean oils come nearer to it than any other oils and 

 are used to supplement linseed oil in the paint industry. At the present 

 time the demand for linseed oil is far greater than can be met by the 

 supply. Were it possible to desaturate other oils such as cottonseed 

 and peanut oil so that they would have the same drying capacity as 

 linseed oil, it would be of enormous benefit to the paint industry. Un- 

 fortunately no method for doing this has yet been discovered, although 

 the reverse process of saturating an unsaturated oil can be easily ac- 

 complished. The term "drying oil" is applied to liquid fats, like linseed 

 oil, which have iodine numbers in the range 150 to 200 and form hard, 

 dry films when spread over a surface and exposed to the air. 



The drying oils are unsuited for lubricating purposes because they 

 tend to become gummy and sticky. The same property of unsaturation 

 operates, but in lubricating oils it is an undesirable property rather than 

 a desirable one. 



Hydrogenation of oils 



The saturating or hardening of fats has become an important com- 

 mercial process. If an oil or soft fat is exposed .to the action of hydrogen 

 in the presence of finely divided nickel (a catalyst) at a moderately 

 high temperature (150° to lOOT..) and pressure (25 lb. per sq. in.), 

 it combines with the hydrogen and is converted into a solid fat. This 

 process is applied annually to several hundred thousand tons of un- 

 saturated fats in the United States. Although not all of this hydrogenated 



