FISH-LIVER OILS 501 



perforated tube. This tube is enclosed in a double cylinder arrangement, and the 

 inside cylinder is perforated. When the inside cylinder is filled with hvers, the kettle 

 is heated. Water in the kettle is boiled and the steam passes through the perforated 

 tube into the livers, releasing the oil which flows into the outside cylinder and 

 is drained off from time to time. 



Flotation Process. At Rimouski, Quebec, one plant is operating in which only 

 cod livers treated with a patented compound (Hopkinson, 1935) known as 

 "Aquacide" (mixture of organic aldehydes, alcohols, and acid) are used. The 

 treated or preserved livers are brought from distant, more or less inaccessible 

 points of production. The preservative appears to harden and "keep" the livers, 

 which can be held in tight drums for several months prior to extracting the oil 

 without appreciable loss of vitamin content. 



This method is not applicable to untreated livers or to those of a number of 

 other families of fish. The livers are removed from the drums, washed with fresh 

 water, and put through a grinder; the ground mass is then passed through a 

 colloid mill, which gives it a consistency approximating that of a thick paste. 

 The product is conveyed into tall, cylindrical, open-top flotation tanks. The height 

 of the tanks is nearly double the diameter; the walls are fitted with rectangular 

 sight glass from the middle almost to the top. Inside each tank is an agitator for 

 stirring; around the walls are perforated pipes at intervals to within a foot of the 

 top. Warm water at about 120° F (40° C) is pumped in through the perforated 

 pipes, and the agitator mixes the water with the ground fish livers, forming an 

 oil emulsion. When the mixture nears the top of the tank, some additional cold 

 water is run in from the top; soon the emulsion can be seen to break and the 

 oil rises to the surface where it is drawn off. The small amount of water in the 

 oil is removed by passing a thin film of the oil through a vacuum drier which 

 operates continuously at a temperature of 75 to 80° F (20.4 to 20.7° C). At this 

 stage any trace of preservative which remained after washing the livers is re- 

 moved. 



There are several critical points which make the flotation process yield almost 

 theoretical. The size of the particle after grinding; the rate of agitation in the 

 tank; the temperature and the rate at which the water is added are all quite 

 critical, and are carefully controlled. 



The dried oil is put through a separator where the last traces of liver pulp are 

 removed. To meet the requirements for refined oil it is chilled to 32° F (0° C) and 

 filtered at this temperature to remove the stearin. It is finally stored in enamel- 

 lined drums under an atmosphere of nitrogen. 



Removal of Oil by Sugar-Beet Residues. Dried sugar-beet residue is mixed with 

 whole fresh livers for extraction of the oil in a patented process (Wentworth, 

 1938). This method is in use in one plant in Canada, and either cod or shark 

 livers can be used in the process. The proportion of beet pulp to livers is 

 governed to some extent by the condition of the livers, that is, the oil and water 

 content and the degree of freshness. An average of 13 pounds of the dried beet 

 pulp is mixed by means of a paddle mixer with 120 pounds of livers. It is not 

 necessary to grind the livers unless they are particularly tough; some species of 

 shark livers require grinding or mincing. After mixing for a few minutes it is 

 possible for an experienced operator to make a test by squeezing a handful of the 

 mass. If the oil is released easily, it is ready for pressing. The mass is placed in 



