No. 3 (1921) MANUFACTURE OF FISH OIL AND GUANO 221 



(3) for washing and heating the separated oil so as to secure 

 further separation and purification by the coagulation and precipi- 

 tation of suspended impurities and by vaporizing suspended 

 moisture. See further under " refinemoit. " 



119- Freeing of the oil from all moisture. — The fourth point is that 

 of the proper drying of the oil. If oil is thoroughly freed from 

 moisture there is much less chance of subsequent deterioration, for 

 such deterioration results from hydrolysis, that is, decomposition 

 effected by water; hence, even if subsequent storage is not well 

 carried out so that the oil is exposed to damp air, well dried oil 

 deteriorates under similar conditions much more slowly than oil 

 which contains moisture, since it takes time for moisture to operate 

 if it has been driven from the mass of the oil and can only attack 

 from the surface ; moreover the enzymes which accelerate decom- 

 position are only active in the presence of water. Further, in the 

 process of drying by heat the oil is usually raised to such a 

 temperature as to destroy bacteria and enzymes, that is, it sterilizes 

 the oil ; consequently well heated and dried oil is almost insuscep- 

 tible of decomposition if decently treated. 



In the United States of America the complete removal of all 

 water is insisted on, but it is not clear whether this is effected by 

 heating except when " refinement " is actually undertaken. In one 

 paper (Greer) it is stated that after the oil has passed " from the 

 last of the series of separating tanks to the cooking tanks it is 

 practically free of water. It is then cooked to the boiling point by 

 steam injected from the perforated pipes placed in the bottom ot 

 the tanks. " The boiling point apparently means that (or some- 

 thing higher) of boiling water (for oil does not really " boil "), but 

 it is not clear why steam is injected through "perforated" pipes, 

 since while driving off, at above 212° F., the slight residuum of 

 moisture in the oil, it must add a great deal more as it condenses 

 in the act of heating up the oil. Probably closed coils are used for 

 this "cooking " ; the process then becomes clear: pressure steam, 

 say at 300° F., heats the oil to above 212° F., and thus drives off as 

 steam any remaining water contained in the separated oil, and, 

 while perfectly drying it, also sterilizes it. But, as shown in para- 

 graph 116 supra, this open steaming is an excellent means of 

 washing and purifying the oil if this has not already been effected. 



The oil at Tanur, being small in quantity and well prepared, 

 washed, separated, and stored in closed vessels — sometimes 



