No. 3 (1921) MANUFACTURE OF FISH OIL AND GUANO 233 



of free acids is immaterial or even — in soap-making — welcome : for 

 other purposes oil should be neutral. Now for edible oils chemical 

 treatment with acids, bichromates, etc., is not permissible, but mere 

 treatment with alkali is not only harmless but highly beneficial. 

 All unrefined oils contain a percentage of fatty acids, from a mere 

 trace in fresh, well prepared oils, to a proportion of even 50 per 

 cent or more; this is specially noticeable in ordinary coast oil 

 after the storage, in mere masonry pits, of oil not properly purified 

 when manufactured. 



This neutralization is readily eifected by mixing with the oil a 

 solution of caustic soda, or, even better, of the carbonate since 

 fatty acids readily combine with the carbonates, which, moreover, 

 are cheaper than caustic and are free from caustic properties. The 

 acidity of the oil is easily ascertained quantitatively by testing it 

 with potassium hydroxide. The ordinary tests for acidity, viz., 

 those of taste or of litmus paper, are insufficient; these tests will 

 prove acidity but not the quantity of acidity, and since there would 

 be considerable loss by saponification or by wastage of alkali if an 

 undue amount of alkali is used, a fairly correct quantitative test is 

 essential. 



132. The improvement of low-class fish oils was referred by the 

 late Board of Munitions (India) to the Rev. Father Caius of 

 Trichinopoly who submitted various reports, the gist of which is 

 that caustic or carbonate of soda improves bad oils. The experi- 

 ments have since been repeated, with additions, at Cconoor with, 

 of course, similar results on acidity, rancidity, and odour, since bad 

 odour depends largely on certain of the acids. The method 

 adopted at Coonoor was as follows: first, steaming with pressure 

 (20 lb.) steam and, secondly, treatment of the steamed oil with either 

 sodium hydrcxide (caustic soda) or preferably, sodium carbonate. 

 The mere steaming resulted in a reduction of acidity by from 25 to 

 50 per cent, the larger relative reduction being in the better classes 

 of oil with only 5 per cent of acidity. The remaining acidity was 

 then neutralized by alkali. It was found that 15 minutes steaming 

 were ample, no appreciable decrease in acidity taking place in 

 longer periods ; steam drives off only volatile acids. 



But it is doubtful whethei such manipulation will pay commer- 

 cially in this country as regards low-class oils ; firstly, even sodium 

 carbonate costs a gccd deal since it has to be imported and carried 

 long distances ; secondly, the process in unskilled hands at the 

 petty factories is apt to be wasteful of oil and alkali ; thirdly, the 



