FISH GLUE AND ISINGLASS 529 



Table 115. Nitrogenous Constituents of Glue. 



Per Cent 

 Protein N 33.4 



Proteose N 42.3 



Peptone N 21.9 



Amino Acid N 2.4 



100.0 



Purified ^ Protein Analysis 



Per Cent 



Ammonia N 5.15 



Melanin N 1.12 



Cystine N trace 



Arginine N 13.80 



Histidine N 2.04 



Lysine N 8.58 



Amino N in filtrate 60.20 



Nonamino N in filtrate 9.66 



100.55 



^ Precipitated with 95 per cent alcohol, redissolved and reprecipitated 4 times. 



Source: Bogue, R. H., "Properties and Constitution of Glues and Gelatin, IV," Chem. 

 Met. Eng., 23, 154-158 (1920). 



Bogue has compared the composition of the amino acid groups of fish glue with 

 that of bone and hide glues. He concludes: 



"This glue (fish glue) shows higher ammonia, melanin, and amino nitrogen of 

 the filtrate, and lower nonamino nitrogen of the filtrate than any other glue, but 

 more nearly corresponds to the low-grade bone glues than to the hide series. Only 

 in its high amino nitrogen of the filtrate does it resemble the latter. The very low 

 nonamino nitrogen of the filtrate in the case of both the fish products indicates a 

 fundamental distinction from animal glues." 



Examination of Liquid Glue 



Many liquid glues are manufactured from materials other than fish stock. 

 Their quality varies greatly; and unfortunately not all the fish glues marketed are 

 of the highest quality. However, this is also the case with hard glues as both bone 

 and hide glues vary widely in properties. Methods of determining the quality of 

 hard glues have been known for many years, but few buyers of liquid glue are 

 able to determine the quality of their glue by analytical methods. For this reason 

 methods of examination of fish and other liquid glues will be outlined in some 

 detail. 



The properties desired in a liquid glue depend upon the use to which it is 

 put. Glue suitable for joining work is considered the best for general use. Special 

 work, such as labeling, requires special glue; since each type of such work calls 

 for a difiFerent quality of glue, it is obviously impossible to consider all of them 

 here. Liquid glues adapted for joining work will therefore be the only ones dis- 

 cussed. 



