198 EXTEACTION OF OILS -WAXES 



linseed, castor. There are three chief methods employed in the ex- 

 traction of oil : 



(1) Pressure ; the most generally employed. 



(2) Extraction by volatile solvents. 



(3) Boiling the bruised seed or fruit with water. 



(1) By pressure. By this method the seeds are cleaned, often de- 

 prived of their husks or shells ("decorticated"), crushed and ground, 

 often heated and moistened, and then subjected to intense pressure in 

 hydraulic presses. The crushed seeds are placed either in horsehair 

 bags or in moulds and are pressed, first at the ordinary temperature, 

 whereby " cold drawn oil " is obtained, and then after heating, " hot 

 drawn oil " is extracted. The oil obtained is refined by heating it to a 

 temperature of about 160 C., in order to coagulate albuminoid matter, 

 and sometimes by treatment with a little sulphuric acid. The residue 

 left in the press constitutes " oil-cake " and usually contains from 6 to 

 15 per cent of oil. 



It is used for feeding or manurial purposes, since, in addition to 

 the oil, it contains the albuminoid and mineral matter present in the 

 seed. 



(2) In extraction by solvents the crushed seeds (in bags or cages) 

 are treated with solvents, such as petroleum naphtha or carbon disul- 

 phide; in such a way that the fresh seeds are treated first with the 

 solvent already highly charged with oil, while the fresh solvent comes 

 first into contact with the seeds, which are almost deprived of oil. In 

 this way, a much more complete exhaustion of the seed is obtained, 

 leaving a residue almost devoid of oil, and therefore of much less value 

 as a feeding stuff than the usual oil-cake. 



(3) Extraction by boiling with water is sometimes used in the ex- 

 traction of castor oil (mainly by the natives of the countries where the 

 seed is grown) and of olive oil. The oil in such cases is merely skimmed 

 off the top of the water. 



The Waxes are substances probably occurring in small quantities 

 in many plants. They are generally analogous to the fats in composi- 

 tion, except that instead of the trivalent glyceryl group they contain 

 monovalent groups; they therefore yield monovalent alcohols on 

 treatment with alkalies. The alcohols obtained in this way are usu- 

 ally complex bodies containing a large number of carbon atoms, e.g., 

 ceryl alcohol, C 27 H 56 O. (?). The waxes are solids melting below 100, 

 non-volatile, and insoluble in water, but soluble in ether. 



Possessing a structure in some respects similar to the fats is a sub- 

 stance, Lecithin, found in many seeds, e.g., beans and peas, and in 

 fungi. This substance, of which probably several varieties occur, has 

 a constitution which may be typified by the following formula : 



f C 18 H 3 A 

 C 3 H 5 C 1S H 3 A 



( HP0 4 .C 2 H 4 (OH).N(CH 3 ) 3 



which may be regarded as the distearyl glycerophosphate of the 

 base, choline, C 2 H 4 (OH).N(CH 3 ) ;3 .OH. 



