CHAPTER 24 



Fish Glue and Isinglass 

 Manufacture of Fish Glue 



Importance and Location of Industry 



The fish-glue industry is one of the minor by-products industries. In 1948 five 

 factories in the United States produced a total of 215,400 gallons. These factories 

 are located in Gloucester and Boston, Massachusetts, in Maine, and in California. 

 Small amounts of fish glue are manufactured in Canada. In England it is made in 

 some fish-scrap factories from the water in which the fish have been cooked. Con- 

 siderable quantities are prepared in Norway and Japan. The great obstacle con- 

 fronting the industry is the difficulty of obtaining a regular supply of suitable stock 

 in sufficient quantities. 



Chemistry of Fish-Glue Manufacture 



The conversion of animal hides and bones into gelatin and glue has been the 

 subject of much research; but little has been published concerning the preparation 

 of fish gelatin and glue. The hydrolysis of fish sounds or air bladders most nearly 

 resembles the manufacture of hide glue, for the tissue dissolves when heated with 

 water; if the resultant solution is evaporated and cooled, a gel is formed which is 

 a gelatin of high purity. Upon hydrolysis most other portions of fish yield glue solu- 

 tions which do not gel at ordinary temperatures; these are called liquid glues. 



Comparatively little is known of the composition of fish skin, scales, and bones. 

 However, it has been found that fish skin and bones contain quantities of collagen 

 and other proteins resembling collagen. The scales of fish also contain much 

 ichthylepidin. Upon careful hydrolysis with steam or boiling water the collagen 

 and related proteins yield gelatin and various proteoses. The percentage of true 

 gelatin formed in the manufacture of fish glue is much smaller and that of proteoses 

 is much higher than in the manufacture of hide or bone glue. Since the proteoses 

 are soluble in cold water, whereas gelatin is not, fish glues are cold water-soluble; 

 but hide glues merely swell in cold water and do not dissolve until the water is 

 heated. 



Source of Raw Materials 



Practically all the fish glue now manufactured is made from the waste products 

 of the cod, haddock, cusk, hake, and pollock fisheries. These fish are the so-called 

 "ground" fish, which are caught chiefly in otter-trawl nets on the banks. Some 

 other species are sometimes used in the manufacture of glue— indeed any fish 

 may be so used— but for several practical and economic reasons other fish are 

 seldom involved. The quality of glue prepared from these ground fish is higher 



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