364 



The World's Commercial Products 



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OLIVE TREES 



running down the sides, 

 or is collected in grooves 

 on the press - plates, 

 whence it runs away 

 to tanks situated below 

 the press. Generally the 

 cake is pressed a second 

 and often a third time ; 

 previous to each ex- 

 pression the cakes are 

 broken up in a cake- 

 breaking machine or 

 ground in the edge 

 runner mill. 



As there is a danger 

 of the cloths ripping, 

 pan presses have been 

 devised in which for the 

 cloths are substituted 

 circular iron boxes or 

 pans. These are packed 

 with meal, and between 

 each there is inserted a 

 circular plate with a conical edge. When subjected to pressure, the plates are forced down 

 on the meal in the boxes, the oil escapes through holes in the inner lining of the boxes, and 

 collects in a circular groove on the plates, whence it runs off to the tanks. These presses are 

 closed and have the advantage that besides doing away with the cloths, the cakes are 

 equally pressed throughout. 



Having described the general method of expression, the process of extraction may be 

 shortly explained. In extraction the solvents used are principally petroleum ether and car- 

 bon bisulphide. Petroleum ether is more dangerous on account of the greater inflammability 

 of -the vapour, but carbon bisulphide produces noxious and poisonous fumes. 



The finely broken-up meal is put into a vessel that is closed down tightly and the ether 

 or carbon bisulphide is introduced ; after passing over the meal and- taking up the oil, the 

 solvent is transferred to a vessel heated by steam, and distilled off, leaving the oil below. 

 The solvent is then condensed and returned to the storage cistern for further use. The 

 oil, not being entirely free from solvent, is subjected to the action of direct steam or a water 

 spray. The chief feature in : the extraction process is to arrange a plant that will work 

 continuously until the oil is ready to be removed. 



The choice between expression and extraction depends greatly upon the use for which the 

 oil or fat is required. For edible oils, such as olive, sesame, earth-nut, expression is necessary ; 

 it is also advisable to express the oil when the cake is intended for feeding purposes. The 

 danger of explosion is a deterrent to extraction, but. on the other hand, by extraction more oil 

 can be obtained ; further, it is freer from mucilage and other impurities and the meal does 

 not so readily become rancid. 



It is impossible within the space at disposal to enter into the methods of refining oils and 

 f ats : . 



DRYING OILS 



Linseed Oil. Linseed is obtained from the flax plant (Linum usitatissimum), also 

 extremely valuable on account of its fibre, which is manufactured into linen. Russia is the 



