236 MADRAS FISHERIES BULLETIN VOL. XIII, 



leaving only the fishy smell belonging to all such oils, but varying 

 from very faint in the best classes to ordinary in the others. The 

 reason is obvious; steaming — -by pressure steam — volatilized 

 certain of the malodorous acids as shown by the loss in weight 

 mentioned in paragraph 132, and the alkali neutralized the re- 

 mainder; scorched, that is, partly carbonized oils retained 

 however their characteristic scorched smell and, of course, 

 colour. Steaming by itself produced great improvement, and in 

 the case of low-class oils this could be adopted without material 

 cost where a boiler is available; it suffices to pass pressure steam 

 through the oil by means of a perforated coil for a certain period; 

 the process not merely deodorizes, but washes and sterilizes the 

 whole mass. As pointed out in paragraphs 32, 35, Il6, steaming is 

 a regular part of the American manufacturing process. 



Hence, where possible, steaming should be resorted to, with 

 the subsequent use of sodium carbonate in the case of oils which 

 it would pay so to treat. High class oils thus treated are perfectly 

 suitable for edible and medicinal purposes where such oils are 

 needed. 



135. Decolorization {Bleaching). — Ordinary Coast fish oil is brown 

 to blackish in colour; the blackish shade is usually due to scorch- 

 ing in the process of cooking and of rude sterilization (in the small 

 private factories) by heating the oil after separation from the mass 

 of water ; see paragraphs 57 and 58 ; this colour, being due to 

 carbonization, cannot be removed. The brown colours are due 

 mostly to delays and imperfections in manufacture as detailed 

 above passim ; some part may be due to slight scorching and is 

 therefore irremediable ; good class oils can be bleached. The 

 American practice is noted in paragraph 40. In the Coonoor 

 experiments (see table in paragraph 133) steaming, followed by 

 neutralization with sodium carbonate, had a very marked eff'ect, 

 bleaching light orange or amber (Tanur) oils in one case to a very 

 pale, almost water-white, oil, and in another case to a pale yellow 

 or light straw colour ; in the case of brown oils there was slighter 

 effect and even this was probably due in general to clarification ; 

 in several cases the oil was slightly darker but much brighter, and 

 the darkening was entirely due to long continued heating in 

 attempts to drive off all residual water. 



The general result of the Coonoor experiments is that decolo- 

 ration by the simple means adopted is but slightly possible with 

 dark common oils, but can be effected to a large extent and very 



