488 MARINE PRODUCTS OF COMMERCE 



and an unsaturated fatty acid of the formula C20H38O2. A large number of fish, 

 liver, and blubber oils contain from 6 to 9 per cent of the glycerides of clupano- 

 donic acid CisHasOa. The free fatty acid is a pale yellow liquid having a fishy smell. 

 Many observers have attributed the characteristic odor of fish oils to the presence 

 of this acid. It has been shown that upon slight hydrogenation of the oils the 

 fishy odor is practically destroyed. Since this is one of the most highly unsaturated 

 acids in fish oil, it is one of the first to combine with hydrogen upon such treat- 

 ment. 



Iodine Number of Fish Oils. The iodine number is an empirical value which is 

 useful in classifying the saturation of the oils. Those having a low "iodine number" 

 are highly saturated and are suitable for inclusion in edible products. Oils having 

 a high iodine number are suitable for hydrogenation and inclusion in products 

 where a drying oil is desired, such as paint, varnish, printer's inks, soap, etc. There- 

 fore, the purchaser is interested in the iodine value of the oil for it gives him an 

 idea of the use to which the oil can be put and assists him in the determination 

 of its market value. The iodine number is useful only in the determination of the 

 degree of saturation of an oU and has no value in differentiation between animal 

 and vegetable oils. 



For purposes of differentiation of fish oils and vegetable oils the bromide test 

 is suggested. Owing to the presence of clupanodonic acid in fish, liver, and blubber 

 oils this test is suggested for the purpose of distinguishing between the drying and 

 semidrying oils. 



Dissolve 1 to 2 g of oil in 40 cc of ether to which a few cc of glacial acetic 

 acid have been added. Cool the solution in a corked flask to 41° F (5°C) and 

 add bromine drop by drop from a finely drawn-out pipette until the brown colora- 

 tion remains permanent. (If the temperature were allowed to rise, evolution of 

 hydrobromic acid would become noticeable. In that case the experiment must be 

 rejected.) After standing for 3 hours at a temperature of 122° F (50° C) the 

 liquid is filtered through a plaited filter, and the precipitate washed 4 times in 

 succession, using each time 10 cc of chilled ether. The residue is finally dried in 

 water over constant weight. 



Clupanodonic acid forms octobromostearic acid (CisHasOaBrs) upon bromina- 

 tion. This substance contains 69.87 per cent bromine, blackens at 392° F (200° C), 

 and decomposes upon further heating. Decomposing before melting may be used 

 as a qualitative test to distinguish between this bromide and linolenic hexa- 

 bromide, as the latter melts at 356 to 357.8° F (180-181° C). Linolenic hexa- 

 bromide is the ether insoluble bromide obtained upon the bromination of fatty 

 acids from linseed oil. Thus, deodorized fish oil may be distinguished from linseed 

 oil and other vegetable drying oils. The ether insoluble bromo derivatives consist 

 of octobromide, hexabromide, or a mixture of both. Since clupanodonic octo- 

 bromide contains 69.87 per cent and hexabromides about 63.32 per cent bromine, 

 the amounts of the respective acids can be calculated from the following two 

 equations: 



x + y=100 



69.87X 63.32t/ 



■+ - = B 



100 100 



