24 U. S. BUREAU OF FISHERIES 
Some 200 samples of salmon oil have been examined to determine 
their physical and chemical properties. These data which are now 
being assembled in report form will indicate to both producing and 
consuming industries the variation in nature of oil obtainable from the 
different portions of the waste and from the several species of salmon. 
For example, the oils varied in iodine number from as low as 104 to 
as high as 225, depending upon the portion of waste and the species 
from which they were prepared. ‘The former oils had some properties 
closely resembling certain edible vegetable oils while the latter were 
more unsaturated than the majority of the best drying oils. With 
such differences in the nature of these oils it is readily apparent that 
present conceptions of salmon oil are not consistent with maximum 
utility. 
EXTRACTION OF OIL FROM HALIBUT LIVERS: 
Increasing interest in fish-liver oils as concentrated sources of 
vitamins A and D has led to a rather general use of many types of 
fish livers for this purpose. Fat livers, such as those obtained from 
cod and haddock and related species give up oil readily by simple 
heat treatment. As a general rule the more concentrated vitamin 
oils are found in fish having lean livers which offer difficulty in extrac- 
tion. 
In our last report reference was made to work on the extraction of 
oil from halibut livers in connection with the preparation of authentic 
halibut-liver oil samples for study by the Food and Drug Adminis- 
tration and the Bureau of Chemistry and Soils. However, because 
of the increasing number of requests for information on methods of 
extracting oil from lean livers, these studies were continued during the 
past year. Asa result a rather simple method with several modifica- 
tions has been developed. This method in general involves a special 
mechanical disintegration of the liver, conversion of the liver into a 
soluble metaproteinate, and separation of the oil from the solution 
by centrifuging. The entire treatment requires less than an hour, 
does not require expensive chemicals or equipment, and gives good 
yields of a pure high quality oil. Details of the method together with 
data on the nature and variation of oil in halibut livers and related 
livers are now being assembled in form for publication during the 
coming year. An application for a public-service patent covering the 
process has been made. 
PREVENTING RANCIDITY IN FISH AND FISH-LIVER OILS 
Beginning November 1, 1935, the Musher Foundation, Inc., New 
York, appointed a research associate in our Seattle Laboratory for the 
purpose of studying the prevention of rancidity and general deteriora- 
tion of fish oils, fish-liver oils, and other fishery byproducts, by treat- 
ment with, or incorporation of, especially prepared cereal flours for 
which the Foundation holds patents. This work was continued during 
1936 and further expanded to include some preserved fishery food 
products. 
Due to the unsaturated nature of the fatty components of fish, fish 
oil, and fatty fish are unusually susceptible to oxidative rancidity with 
the resultant development of off odors and flavors. Numerous 
chemical compounds have been found to possess antioxidant proper- 
ties, i. e., retard oxidative rancidity, but most of these are not suitable 
for use in foods. Accordingly, food industries are anxious to find 
