No. 3 (1921) MANUFACTURE OF FISH OIL AND GUANO 219 



116. As shown above, in the United States of America the 

 mixed water and oil pass into settling tanks where the solid and 

 comparatively massive impurities specially fall to the bottom and 

 are eventually removed and utilised as " gurry " by removal of the 

 oil and subsequent drying of the scrap. The oil with its dissolved 

 and suspended impurities then passes into other tanks in series 

 where the oil and water gradually separate, the process being 

 accelerated by raising the temperature in the tanks to 150° F. or 

 higher, with the result— though this is not directly stated — that 

 the albuminous matter is coagulated, since albumen coagulates at 

 above 140° F. : the coagulated substances are precipitated and in 

 their precipitation carry down with them suspended impurities. 

 A further result of the steam heating when effected by open steam, 

 is to wash the oil mechanically and, by the condensation of the 

 steam as pure boiling water, to dissolve out from the oil any 

 dissolved impurities seeing that these are readily soluble in hot 

 water but sparingly soluble in oil where indeed they may be 

 suspended rather than dissolved. Open steam heating by which 

 fresh water is added to the oil, necessitates further separation of 

 water, but this is part of the purifying process since the water is 

 clear water when condensed from the steam and only becomes 

 foul by dissolving and removing impurities; still, being rendered 

 impure, it must also be separated as quickly as possible. The heat 

 of the steam also tends to cause rapid separation since the specific 

 gravity of the oil is lowered by heat to a greater degree than water. 

 Moreover this heating, especially if carried up to ordinary boiling 

 point, and possibly even lower, destroys any bacteria, as well as 

 the enzymes or chemical ferments which cause hydrolysis and the 

 formation of fatty acids and therefore rancidity. The oil thus 

 largely purified is rapidly withdrawn from the upper parts of the 

 settling tanks by syphons, swivel pipes, etc, and the remaining 

 water-cum-oil is again passed into a further tank, and so on. The 

 nature of the settling pits or tanks has been described above. 



In many factories the semi-purified oil is passed through filters, 

 whether filter presses or ordinary filters as elsewhere described 5.1;. 

 ''filtration'' ; this effectually removes any solid or coagulated 

 impurities and with them the bulk of the agencies, which tend to 

 act upon the oil. 



117. This process is followed, mutatis mutandis, at Tanur, but 

 the receiving and settling pits or metal separators are not provided 

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