FATS AND OILS, WAXES, AND LIPOIDS 137 



of carbohydrates to fats, and vice versa, which take place in both 

 plant and animal nutrition. 



THE EXTRACTION OF OILS FROM PLANT TISSUES 



There are three types of methods which are employed for the 

 extraction of oil from oil-bearing seeds, etc., either as a com- 

 mercial industry or for the purposes of scientific study. These 

 are (1) by pressure; (2) extraction with volatile solvents; and (3) 

 boiling the crushed seeds or fruits with water. 



By the first method, the seeds are first cleaned, then " decor- 

 ticated " (hulls removed), crushed or ground, then subjected to 

 intense pressure in an hydraulic press. In the commercial process, 

 the ground seeds are first pressed at ordinary temperature, which 

 yields " cold-drawn " oil, then the press cake is heated and pressed 

 again, whereby " hot-drawn " oil is obtained. The crude oil is 

 refined by heating it to coagulate any albumin which it may 

 contain, and is sometimes bleached by different processes before 

 it is marketed. The press cake from many seeds, such as flax- 

 seed (linseed), cottonseed, etc., is ground up and sold for use as 

 stock feed. 



In the second method, the finely crushed seeds are treated with 

 solvents such as gasoline or carbon bisulfide, in an apparatus which 

 is so arranged that the fresh material is treated first with solvent 

 which has already passed through various successive lots of 

 material and has become highly charged with the oil, followed 

 by other portions which contain less oil, and finally by fresh sol- 

 vent, whereby the last traces of oil are removed from the material. 

 The saturated solvent is transferred to suitable boilers and the 

 solvent distilled off and condensed for repeated use, leaving the oil 

 in the boiler in very pure form. 



Extraction by boiling with water is sometimes used in the 

 preparation of castor oil and olive oil. In such cases, the crushed 

 seeds are boiled with water and the oil skimmed off as fast as it 

 rises to the surface. 



IDENTIFICATION OF FATS AND OILS 



Fats and oils are identified by determinations of. theft physical 

 properties, such as specific gravity, melting point, refractive 



