FISH ISINGLASS AND GLUE. 15 



Lambert '^ discusses fish glue and describes its manufacture as 

 follows : 



The fish offal is carried by conveyors to a series of washing tanks placed 

 overhead, and thoroughly washed with water to remove the blood, etc. From 

 thence it falls by gravitation into tlie digesters, and is heated with "live" 

 steam for 10 hours. The oil and gelatinous water are drawn off by a pipe fixed 

 to the bottom of each digester, into tanks, the oil skimmed from the surface, 

 and the glue liquors clarified with a small portion of alum. On filtering they 

 are concentrated in open vats provided with a steam coil, to a strength of 82 

 per cent dry glue, and then bleached with sulphurous acid. The residue in tlie 

 digester is converted into guano. 



Fish glue is a light brown viscous liquid with offensive odor and acrid taste. 

 It forms a sticky mucilage when diluted with water, and as met with in com- 

 merce, already contains about one-half its weight of w^ater and such liquid is 

 weight for weight, only about equal to a dextrine in viscosity. 



The ash of fish glue is comparatively high, about 4 per cent on body dried 

 at 100° O. It is usually white in color, and has besides carbonates of calcium 

 and potassium, some 5 to 10 per cent phosphate of calcium. Fish glue is said 

 to assume a greenish-yellow color on boiling with potash and absorbs about 9 

 per cent of the caustic. Liquid gums of this class are easily distinguished by 

 boiling with Fehling's solution, when they assume a violet color, and by the 

 tannic-acid reaction. The best method to remove the unpleasant odor and 

 taste of fish glue is to boil the solution in a little water with 1 per cent phos- 

 phate of sodium and to add 0.25 per cent of saccharine. 



The offensive odor of fish glue may also be disguised by the addi- 

 tion of creosote, oil of sassafras or wintergreen, or other substance 

 with a strong odor. 



There have been several methods proposed for the testing of glue, 

 none of which are perfectly satisfactory. Among the more common 

 tests are those of the viscosity and consistency of the jelly formed. 

 The adhesive power of the glue, however, does not depend on the 

 character of the jelly entirely. Glue is sold with regard to its 

 physical properties, especially its color; all fatty matter should be 

 absent. 



• Lambert, T., 1905 : " Glue, gelatin, and their allied products." London. 



