184 U. S. BUREAU OF FISHERIES 



approaching the normal concentration of the oil in the liver or it may 

 be used in fortifying the foreign oil to any desired degree below this 

 potency. 



Vitarnin testing methods. — For a number of years the antimony 

 trichloride color reaction has been a popular method for estimating 

 the vitamin A potency of fish-hver oils and finds usage as a control test. 

 However, the method has been subjected to such a great amount of 

 criticism that many investigators consider the test to carry no degree 

 of reliability. In spite of this criticism, there are others who have 

 found the method useful and continue to use it, taking cognizance of 

 its reported liinitations. One of the principal criticisms of the method 

 is that there is no consistent relationship between Blue value (colori- 

 metric method) and Biological value as determined with rats. In 

 this case, however, the data are generally viewed from the standpoint 

 of a direct comparison. 



During the course of our liver oil studies, Blue unit values have been 

 obtained on a relatively large number of liver oil samples having 

 vitamin A potencies varying between 5,000 and 200,000 U. S. P. units 

 per gram as determined by biological assay. In studymg these data, 

 there was found to be a definite power relationship between the two 

 types of values. In applying this correction it has been possible to 

 increase the accuracy of the test. 



FISH OILS IN PAINTS 



During the past year, as a result of conferences of our technologists 

 with members of the industry, there was a greatly increased use of fish 

 oils in paints. Not only did this increase extend to the lower grades 

 of paints, but, for the first time in the history of the paint industry, 

 some of the leading paint manufacturers made extensive use of fish 

 oils as ingredients of the higher priced paints and this fact was widely 

 advertised in trade journals. This development can be attributed 

 largely to improvements in the refining of fish oils by some of the 

 leading refiners of the country, with the cooperation and assistance 

 of our technologists. 



STUDIES ON FAT IN FISH MEAL 



As fish meals have become more widely used and their properties 

 more thoroughly understood, the question of fat content has likewise 

 become an important consideration. The reason for this is that the 

 amount of fat present is an indication of the proportion of the material 

 which may be subject to oxidative deterioration. Consequently, low 

 fat content meals are preferred by some consumers and sale may be 

 predicated upon this factor. Unfortunately, however, the fat, or 

 more correctly the oil, becomes less soluble in normal solvents when 

 oxidized, and oxidation may, therefore, lead to an apparent decrease 

 in fat content. Furthermore, accepted practice for determining fat 

 is not uniform. The unsatisfactory nature of this situation is ob- 

 vious because a meal reported as having a low solvent extract value 

 may have reached this condition as a result of oxidative deterioration. 



For some time the Bureau has appreciated the need for tests which 

 will clarify this confusing condition, because such information would 

 not only lead to more satisfactory methods of control in marketing 



