128 THE FISHING INDUSTRY 



oleic. Palmitic and stearic acids and their compounds 

 are solids at the ordinary temperature, whereas oleic 

 acid and its compounds are liquid. This difference 

 appears to be connected in some way with the molecular 

 structure of these substances. When oleic acid is heated 

 with hydrogen gas under pressure, in the presence of 

 finely-divided nickel, it absorbs hydrogen and is trans- 

 formed into stearic acid. Oleic acid, therefore, is said to 

 be unsaturated with respect to hydrogen, whereas 

 stearic acid is called a saturated acid. This process, 

 whereby a liquid oil is transformed into a solid fat, is 

 called hydrogenation, or hardening. 



Both the margarine industry and the soap industry 

 require large quantities of hard fats. Originally the 

 soap industry absorbed the available supplies of hard 

 animal fats such as beef suet, hog's lard, and mutton 

 suet. The margarine industry depended upon these 

 same supplies of animal fats, and the rapid growth in 

 the production of margarine during recent years has 

 seriously diminished the supply of hard fats necessary 

 for the manufacture of soap. 



The hydrogenation of whale oil and various fish oils 

 has now made it possible to supply this demand, and 

 has also made possible the industrial utilization of 

 substances, such as fish oils, for which formerly 

 comparatively little use could be found. 



Hardened whale oil melts at 40 to 50C., and is a 

 white solid entirely devoid of taste or smell. It is used 

 for making soap, and as a lard substitute for cooking 

 purposes. 



Fish Glue. Fish glue is the most important liquid 

 glue on the market. The bulk of the fish glue manufac- 

 tured to-day is made from the waste and offal that are 

 discarded by the curers. This waste consists of heads, 

 bones, viscera and skins. The best glue is obtained from 



