PROPERTIES OF GELATINE AND GLUE 219 



as those of the finger test. The method, however, is much 

 more laborious than the " finger test." < 



Gelatine is also graded according to the results of bleach- 

 ing and clarifying, but with quite arbitrary standards, 

 largely determined by the fancy of the customer. 



Chemical analyses, involving estimations of ash, lime, fat, 

 acid, water, insoluble matter, and poisonous metals, e.g. 

 arsenic, copper, zinc and lead, are of value for special cases 

 according to the destiny of the goods. Special physical tests, 

 such as " breaking strain " and " foam test," are also of some 

 little value in special cases. 



REFERENCES. 



" The Chemistry of Colloids," W. W. Taylor. 1915. 



" Handbook of "Colloid Chemistry," W. Ostwald. 1919. 



" Chemistry of Colloids," Zsigmondy and Spear. 1918. 



" Introduction to the Chemistry and Physics of Colloids," E. Hatschek. 



" Surface Tension and Surface Energy," Willows and Hatschek. 



" Chemistry of Colloids," V. Pose hi. 



" Grundziige d. Dispersoid Chemie," von Weimarn. 



" The Lyotrope Series and the Theory of Tanning," Bennett, J.S.L.T.C., 

 1917, p. 130. 



" The Swelling of Gelatine," Bennett, J.S.L.T.C., 1918, p. 40. 



'"' The Swelling of Gelatine," Procter, J.C.S. Trans., 1914, 105, 313 ; and 

 Kott. Chem. Beihefts, 1911, 2, 234. 



" The Swelling of Gelatinous Tissues," Procter, J. S.C.I., April 16, 1916. 



" Summary of Procter's Views, and Bibliography," Collegium (London), 

 p. 3, 1917. 



" Lyotrope Influence and Adsorption in the theory of wet work," Bennett, 

 J.S.T.C., 1920, p. 75. 



For the " finger test," see 



" Glue and Glue Testing," Rideal, 2nd ed., p. 158. 



" Leather Trades' Chemistry," Trotman, p. 241. 



