FISH ISINGLASS AND GLUE. 9 



small pieces. This material is then further mixed and macerated 

 between a set of iron rollers, from which it passes to so-called sheet- 

 ing rollers. These are the hollow iron rollers, cooled by water and 

 provided with a scraper, as mentioned above. The gelatin is con- 

 verted into sheets one-eighth to one-fourth inch thick, 6 to 8 inches 

 wide, and of variable length. These sheets are finally passed 

 through ribbon rollers until the ribbons produced are one-sixty- 

 fourth of an inch thick ; the width is the same as that of the sheets. 

 The ribbons are dried in a few hours by being suspended in mod- 

 eratel}^ warm, light rooms; they are then rolled on wooden spools 

 into coils weighing less than a pound each. About 20 per cent of 

 the weight of the original sounds is lost during their conversion into 

 isinglass. 



A product called transparent or refined isinglass is manufactured 

 by dissolving New England isinglass in hot water and spreading the 

 solution to dry on oiled cloth. Very thin, transparent sheets are 

 thus produced, and these yield an excellent grade of glue, but retain 

 a rather pronounced fishy odor. 



When the best grades of isinglass are treated with hot water, they 

 swell uniformly, produce an opalescent jelly, and finally entirely 

 dissolve. Isinglass is insoluble in alcohol, but readily soluble in 

 most dilute acids and alkalies. A^Tien ignited, isinglass should yield 

 no more than 0.9 per cent ash, whereas poorer grades of fish glue, 

 or gelatin, yield from 1.5 to 4 per cent ash. 



Isinglass has been adulterated by rolling a layer of gelatin between 

 two layers of isinglass. Such adulteration may be detected by 

 treating with water and observing the nature of the colloidal solu- 

 tion under the microscope. Isinglass retains its characteristic fibrous 

 structure which is not present in a gelatin solution ; the gelatin be- 

 comes more transparent than before, the shreds being disintegrated. 

 Both of these effects would be observed in the adulterated article. 



The results of the analyses of some different forms of isinglass 

 are presented in the following table f 



Source of isiBslass. 



Astrakhan . 



Source of isinglass. 



Hamburg 



Iceland 



East India 



Yellow, unknown 

 source 



Residue 



insoluble 



in hot 



water. 



Per cent. 

 2.3 

 5.2 

 21.6 

 8.6 



15.6 



It may be readily observed that the Russian isinglass (Astrakhan) 

 is by far the best of those samples analyzed. 



" Prollius, I. F. : Abs. Journal of the Chemical Society, p. 647. 1884. London. 



