l80 MADRAS FISHERIES BULLETIN VOL. Xlll, 



act mechanically by carrying down impurities as they sink through 

 the oil ; moreover dry salt absorbs water as it passes through the 

 oil. The oil may be washed once or twice, the water being poured 

 through fine sieves placed over tall separators, or the water may be 

 agitated mechanically with the oil and allowed to subside or, per- 

 haps best of all, pressure steam may be let in from open coils ; the 

 steam condenses in the oil and thus supplies the necessary hot 

 water; the great heat from the condensing steam thoroughly 

 sterilizes all organic impurities, while the jets of steam violently 

 agitate the mass and thoroughly wash the oil. The washed oil is 

 then separated as above. 



It may seem strange to add washing water in quantity after 

 taking trouble to separate the oil from the original water, but 

 though the process is somewhat troublesome and involves a second 

 separation it is not only worthwhile but necessary if good class oil 

 is to be made and a good price obtained. In America this is not 

 only a regular operation but the storage tanks are often left 

 uncovered in the open so that the contents may be washed by the 

 pure water of the rainfall : this might be adopted in India : more- 

 over, the strong sun bleaches the oil in some degree, and also tends 

 to revaporize much of the water. 



72, After washing a further process may or may not be adopted ; 

 inTanur it has not been found necessary since the oil has not been 

 in large quantity and is always thoroughly washed, so that it then 

 keeps good, with minimum deterioration from hydrolysis, if stored 

 in closed receptacles (in tall iron tanks or in closed kerosine tins) 

 where it is unaffected by light and air which tend to cause acidity 

 and rancidity in impure oil exposed to them. This further process 

 is that of heating the oil slightly above 212° F. so as to drive 

 of any residual suspended moisture. As mentioned above the 

 imperfect practice of the coast " factories " is to apply the heat of 

 an open fire to a mass of viscid oil with the certainty of scorching 

 much of the oil and thereby spoiling it in colour and odour; 

 moreover the moisture is imperfectly driven off. With steam, as at 

 Tanur, this can readily effected without scorching, or even deepen- 

 ing the colour of the oil ; a closed steam coil heats the oil in a tub 

 or tank to the required degree, say 215° to 220° F. when the mois- 

 ture in the oil is necessarily vaporized. Other steam methods are 

 obvious ; an elegant apparatus at Tanur consists of a tall galvaniz- 

 ed iron vertical cylinder, provided internally with a spiral closed 



