FIXED OILS AND WAXES 73 



perature. They arc insoluble in water and in cold alcohol, 

 somewhat soluble in hot alcohol, easily soluble in ether, 

 chloroform, carbon tetrachloride, carbon disulphide, and 

 other volatile solvents. They "saponify" on treatment with 

 alkaline hydroxides, that is, they break up into glycerine 

 and the alkaline salt of the fatty acid, called a soap (Section 

 ()b). They hydrolyze to glycerine and fatty acids on treat- 

 ment with steam, and also under the influence of lipases 

 (Section 8). 



They are found for the most part in the seeds of plants, 

 where they serve as reserve material for respiration, or from 

 which to make carbohydrates (Sections 8 and 32). Fixed 

 oils are, however, found in all living cells of plants and 

 apparently play a necessary part in the functioning of 

 protoplasm. 



The fixed oils are "drying" or u non-drying" in character. 

 That is, on exposure to the air some of them absorb oxygen 

 and harden more or less, while others remain perfectly liquid. 

 This is a property of the fatty acid radicle. The non-drying 

 oils on exposure to the air slowly become rancid, that is, 

 oxidation takes place, helped by the action of bacteria, which 

 gives the oils a disagreeable smell and taste, and makes them 

 acid to litmus. This is due to the formation of free fattv 

 acids with some other products. 



65. Methods of Extraction. — An old way of extracting 

 fixed oils from seeds and other plant substances was to crush 

 them and boil with water. The oil rising to the top could 

 be skimmed off. Another way is to extract the oil with 

 volatile solvents which can later be distilled off, leaving the 

 oil behind. This process, however, is expensive and the 

 product contains other compounds which dissolve out in 

 the solvent and remain as impurities in the oil. 



The most common method is to clean and decorticate the 

 seeds (remove the husks), place them in bags and squeeze 

 the oil out by heavy presses. The first expression is made 

 in the cold which gives a better quality of oil. The pulp 

 is then expressed hot and more oil is obtained, but it is not 

 so pure. The material remaining is called 'press cake," 

 and when ground is sold for cattle food and fertilizers. 



