BY-PRODUCTS OF FISHERY INDUSTRIES 227 



given to the tanning of the skins of true fishes. It 

 required the services of the modern chemist to make 

 leather from shark skins, for the outer covering is 

 very hard and difficult to remove. This hard rough 

 coating, called shagreen, was formerly used as an 

 abrasive and for sword-hilts. Until the scientist 

 studied the problem, the only known way to remove 

 the shagreen was to scrape the surface with a heavy 

 rasp or file. According to the more up-to-date pro- 

 cesses the skins are first tanned with a vegetable tan- 

 ning extract, and then the shagreen is removed by 

 milling with an acid solution. Inasmuch as the 

 shagreen is calcareous in nature, this treatment 

 quickly removes it. After the removal of the rough 

 coating, the tanned skins are then treated with cer- 

 tain fatty liquors which make them soft and pli- 

 able. 



A slightly different process is carried out in pro- 

 ducing chrome tannage. In this case the shagreen is 

 first removed, after which the skins are pickled in 

 dilute acid and then placed in the tanning solution, 

 which contains a basic salt of chromium. After tan- 

 ning is complete, the skins are treated with a soda 

 solution and then dyed. 



The shark fishery has been of much assistance to 

 the other fisheries, as sharks are very destructive of 

 the relatively frail nets set for other fishes, often 

 tearing them to pieces. The sharks are usually caught 

 in wire nets, which are so strong that they cannot be 

 torn, and which have such large meshes that the 

 smaller fish can pass through. 



North Carolina and Florida are the centers of 



