232 MADRAS FISHERIES BULLETIN VOL. Xlll, 



appreciable darkening where the oil is of a fine yellow colour ; such 

 darkening will lower price when the oil is required for edible 

 purposes for which a light or bright yellow is always desirable. 

 One text book recommends the "gentle" heating of the oil " by 

 steam pipes to a temperature not higher than 50^C. (I22°F.) while 

 a current of air is blown through " , probably the air is warm, and 

 the friction of the air currents increases the heat. In the Tanur 

 Yard there is a m.ichine for this purpose consisting of a strong 

 galvanized steel vessel closed air-tight above and provided with 

 {(j) a closed tinned copper steam coil inside for heating the 

 contents, (/;) a Korting steam air-ejector at the top of the vessel, 

 (r) a perforated copper coil inside the vessel at the bottom and 

 communicating with the outer air. The vessel is two-thirds filled 

 with oil and closed air-tight; steam is then turned on through (^7) 

 till the oil is sufficiently heated as above ; (b) is then set to work, 

 and by causing a partial vacuum within the vessel (upper part) 

 air is sucked through (c) and passes in numerous rapid currents 

 through the warm oil which it further heats by friction. The air 

 should be dry and warm for the best effects. The oil is said to be 

 greatly brightened by this process, obviously by dehydration. 

 The machine however has never been used since refinement has 

 not been practised there. 



131. Neutralisation.— So far the " refining '' processes which 

 have been considered are those advisable with all classes of oil 

 to fit them for the particular market for which their ciualities suit 

 them, and also to prevent deterioration while awaiting such market 

 or subsequent use ; filtration indeed is not so necessary, but is 

 merely adopted to ensure rapidity and completeness as against the 

 gravity settling method. But where high-class oils are desired, as 

 for edible and medicinal oils, or in leather preparation, or for 

 "browning" etc., work in arsenals, or for hydrogenation, it is 

 necessary further to improve oils as in the process mentioned 

 below; acid oils are not permissible for edible goods or for 

 hydrogenation ; good colour is necessary in edible oils, and the 

 only permissible odour is the slight fishy odour similar to that 

 observed in good cod liver oil ; moreover, acidity is a precedent of 

 rancidity. Hence neutralization, that is the removal of fatty acids 

 and the general improvement of good class oil, mainly for edible 

 and medicinal purposes, is advisable. For ordinary technical 

 purposes (jute batching, steel tempering, soap-making), the presence 



