No. 3 (1921) MANUFACTURE OF FISH OIL AND GUANO 237 



readily by steaming and neutralization in the case of good oils 

 when, however, it is not always desirable, since a bright yellow oil 

 generally meets public demands better than a pallid or very pale 

 oil- 



136. In Tanur it was attempted to bleach orange coloured oil 

 by exposure to the sun but no perceptible effect was produced 

 after exposure even for weeks, probably because air was excluded 

 during the process. But from the decided statements in the text 

 books it would seem that where bleaching is desirable, this simple 

 and cheap method should be again tried and more thoroughly, 

 since tropical sunlight should be specially powerful. The method 

 as described in one text book is to place the oil in glazed boxes or 

 frames (e.g., of window glass set in frames) of perhaps 4 inches in 

 depth ; both sides of the boxes are glazed so that the sunlight passes 

 clear through the oil. A necessary condition is a supply of air; 

 hence the upper part of the box which is closed to prevent impuri- 

 ties falling in, is perforated below the cover to allow of free perfla- 

 tion of air over the surface of the oil. It is said that in 14 days 

 the oil will become white and clear. To hasten or ensure sun- 

 bleaching the addition of certain chemicals is said to be effica- 

 cious, but this is not permissible for edible or medicinal oils. 



The process is suggested for "oils" in general, but fish oils are 

 not expressly mentioned. 



137. In the rare cases, e.g., paints, where fish oil may require 

 bleaching for technical (non-edible) purposes, chemical bleaching 

 is possible, for which the text books must be consulted ; probably 

 sodium sulphite is the cheapest, easiest, and most innocuous che- 

 mical, but no experiments have been made with it or other chemi- 

 cals. It is expressly stated that chlorine darkens fish oils. 



Decoloration is mostly needed for edible and medicinal uses 

 and, to some extent, for hydrogenation. Fish oil is not generally 

 used as oil in ordinary soap making as it is difficult to disguise its 

 very persistent odour, so that it is almost entirely used for saddle 

 soap and insecticidal soaps in which colour docs not matter. 

 For hydrogenation the oil should be a good yellow iiciilral oil, and 

 this loses its specific odour when hydrogenated, forming a white, 

 almost inodorous, fat ; it then becomes useful, in the place of 

 tallow, for ordinary soap making. In leather working and for 

 paints and use in arsenals the colour should be yellow to light 

 brown, but for ordinary technical purposes such as jute batching, 



