From the data given above it was evident that in the sample of menhaden oil used there were present highly unsaturated acids other than clupanodonic acid. Five fish oils which were available were analyzed to determine the probable nature of the highly unsaturated acids. The constants of the oils are given in Table III.

Table III

Analytical Constants of Commercial Fish Oils

Oil

Sap. No.

Iodine No.

n20°

Menhaden ............

191.2

151.7

1.4778

Salmon ............

185.0

137.2

1.4768

Cod ...........

186.9

151.0

1.4770

Herring ...........

186.5

139.8

1.4765

Sardine ........

187.3

158.1

1.4791

One kg. of each oil was esterified by the method mentioned previously and the methyl esters were distilled into fractions over a 10° range under 15 mm. pressure. In the case of menhaden oil 3 kg. was used and the distillation repeated thrice. The fractions were then analyzed for free acid, mean molecular weight of the acids, index of refraction, iodine number, polybromide number and percentage of bromine in the bromides, while the mean molecular weight of the acids was calculated from the molecular weight of the esters as determined by saponification.

The fish oils examined were found to be decidedly similar in character. In general the iodine number, polybromide number and percentage of bromine in the bromides increased with the boiling point, the main divergence being in the last fraction, which might easily contain decomposed material.

The oils as a class contain acids whose esters distil at much too high a temperature for the C18 series. Among these higher acids are those which are more highly unsaturated than clupanodonic acid.