214 MADRAS FISHERIES BULLETIN VOL. XIII, 



111. Hence the^zr^^ point to be attended to in obtaining fish oil 

 (and guano) is the avoidance of taint in the fish whether by 

 insisting on freshness or by the use of a preservative such as salt. 

 To this end (and for sanitary reasons and to avoid public nuisance) 

 factories should make arrangements, if possible, that the fish 

 should be brought to shore as soon as caught, e.g., by carriers, and 

 at once dealt with ; this conduces also to efficiency and superiority 

 of product since it distributes the work over a longer period and 

 does not crowd operations or tire workers. Moreover, factories 

 should not attempt to deal with larger quantities than can be 

 worked off in, say, 12 hours ; further, it is strongly advisable that 

 the latest received batches should be mixed with salt, say I lb. of 

 salt to l6 lb. of fish, to inhibit taint while waiting. If the fish are 

 to be kept any further length of time, a larger proportion of salt, 

 say I to 12 or even I to 8 should be used when they will keep fairly 

 well for a short time, but not for long since they are ungutted. 

 The presence of salt is otherwise advantageous, since oil separates 

 more rapidly from salt water of specific gravity greater than that 

 of pure water. 



112. Rapid separation of oil from the Jisli. — The second point to be 

 mentioned is the advisability of rapid separation of the oil from 

 the mass of fish ; by long heating in contact with the tissues, or by 

 leaving the oil for a few hours in contact with the boiled mass, the 

 oil not merely darkens in colour but, which is more important, 

 absorbs or takes up proteid and other matters which are foreign to 

 the oil and will rapidly decompose in the oil, thus producing not 

 only the malodorous decomposition products above mentioned but 

 assisting the water in the oil to decompose (hydrolyse) the oil 

 itself, thus producing acidity and rancidity. 



If fat fish are boiled with a considerable quantity of water so 

 that the oil may come rapidly to the surface, the oil on first 

 appearance, a few minutes after beginning operations, is so limpid 

 and colourless as to be observed with difficulty ; a little later it 

 becomes yellow ; if then skimmed or run off with the surface 

 water, at once separated from the water, and then washed with 

 boiling water, preferably saline, the resulting oil is A I, ordinarily 

 needs no further refining, has been described as " unique," and is 

 fit for and has often been used for edible and medicinal purposes ; 

 it may however be rendered softer and more bland by treatment 

 with alkali, as shown below. 



