248 FISHERY INDUSTRIAL PRODUCTS 



pearl essence plants in Maine. The herring are transported from the traps 

 to the cannery in boats provided with special false bottoms which furnish 

 a means for collecting the scales that are removed by the fish as they 

 thrash about in the vessel. The guanine material is sometimes separated 

 from the scales in an agitator with water which is then centrifuged from 

 the guanine crystals^ In other cases the scales, which may remain on the 

 fish until after they reach the processing plant, are separated from wash 

 water within the canneryl The crude guanine is generally next treated in 

 acid solution with pepsin for about 48 hours. This digests much of the 

 proteinaceous impurities. The guanine crystals may be suspended in 

 water containing a little ammonia. More frequently they are dispersed 

 in a nitrocellulose ethyl acetate lacquer. 



Many efforts have been made, without complete success, to develop a 

 synthetic guanine pearl essence product. Earlier this failure was ascribed 

 to difficulty in getting the proper crystal size for the guanine to reflect 

 the light in the most advantageous way. According to Decker^, the par- 

 ticularly effective sheen from pearl essence made from fish scales is due 

 to the retention of an envelope of hydrolyzed protein around the guanine 

 crystals. Therefore, the optical effect of irridescence is a combined prop- 

 erty of the hydrolyzed protein envelope and the guanine crystals. The 

 pepsin digestion and other processing steps, if carried too far, will remove 

 some of this proteinaceous envelope and thus reduce the desired irri- 

 descent properties of the pearl essence. It is, therefore, important to ob- 

 tain the fish scales in a condition as free from impurities as possible, so as 

 to reduce to a minimum the handling and processing steps. While pres- 

 ence of blood, dirt, and other foreign impurities reduces the quality of 

 the end product, excessive processing to remove them may result in loss 

 in quality of the pearl essence. 



Clam and Oyster Shell for Poultry Feed. Oyster shells are commonly 

 dried and ground for use in poultry feed. The shell is first dried, usually 

 in an indirect flame dryer, and then passed through a grinder which may 

 be of the hammer mill type. From the grinder, the material passes through 

 a series of vibrating screens and may be sacked according to different 

 mesh sizes or reground to a finer size before sacking. In some locations, 

 e.g.. Southern California, huge deposits of dead clam shells are located in 

 tide flat areas. These are ''mined" by being dredged up with large steam 

 shovels at low tide when they are exposed and dried and ground similarly 

 to the preparation of the product from the oyster industry. Thousands of 

 tons of such clam shells have been removed from these beds and the 

 supply in some areas seems to be almost inexhaustible. 



Pearl Button Industry. Marine and fresh water shells are used to manu- 

 facture buttons and other items such as belt buckles. In general, in the 



