82 American Fisheries Society 



unstable compounds without breaking them up. Ordi- 

 nary distillation decomposes the oils, changes their com- 

 position, and the almost hopeless mixture of giycerides 

 presents a very complex problem to the analytical chem- 

 ist. The drying power of the oils is shown by the iodine 

 numbers. The iodine number is the percentage of iodine 

 absorbed by an oil, and is probably the constant which 

 tells more of the value of the oil than any other. While 

 many of the fish oils have iodine numbers nearly as great 

 as that of linseed oil, they do not necessarily dry in ex- 

 actly the same manner, a sticky gum being sometimes 

 obtained instead of a hard, dry film. 



Many attempts have been made to refine fish oils and 

 rid them of their fishy odor, taste and color. Very few 

 of these attempts have met with any degree of success. 

 Physical methods may include washing with water and 

 drying either by allowing to settle, or drying with cal- 

 cium chloride, cooling to separate "stearine," allowing 

 to stand over or filtering through fullers' earth, infusorial 

 earth, or animal charcoal, and steaming under ordinary, 

 reduced, or increased pressure. As far as my observa- 

 tions go, the use of such agents as charcoal do not change 

 the character of the oils to any appreciable extent, espe- 

 cially if they are of fairly good quality to start. The 

 results of steaming oils will be considered later. 



Chemical methods of purification may be used, al- 

 though very few of these attempts have met with any 

 degree of success. The oil may be treated with a small 

 amount of concentrated sulphuric acid and the slightly 

 charred product allowed to settle, the albuminous im- 

 purities thus being dragged down. I have found this 

 process practically worthless for marine animal oils. 

 Treatment with ozonized air, and chlorine generated in 

 various ways, have been tried, as well as very many other 

 processes. That process which seems at present to prom- 

 ise ultimate success is the so-called hardening of the oils 

 by hydrogen. 



"The treatment of unsaturated oily bodies with hydro- 

 gen to obtain saturated derivatives is of great scientific 

 and technical interest. In the fat industry a most fas- 



