BLEACHING 247 



agents. Its application is simple, a concentrated solution 

 being added to the gelatine sol before or after evaporation. 

 It is the most " fool-proof " of all the oxidizing agents used 

 in bleaching, and it yields the purest product. Its bleaching 

 action is perfectly satisfactory, but only in a non-acid sol. 

 Hydrogen peroxide is moderately stable in acid solution, and 

 its bleaching action is best in slightly alkaline solution. 

 An acid sol bleaches too slowly, or not at all ; an alkaline sol 

 induces evolution of oxygen and consequent waste. The 

 great disadvantage of peroxide of hydrogen is its great 

 expense, which is enhanced by an increasing demand for 

 it in other industries. A minor disadvantage is its instability, 

 which leads to loss in transit and storage. It is sold usually 

 in strengths indicated by the volume of oxygen obtained 

 from unit volume of the solution, when treated with per- 

 manganate in a nitrometer (e.g. " 15 vols. peroxide "). 



It is a fortunate feature of both the oxidizing and reducing 

 agents usually employed in bleaching, that they have con- 

 siderable antiseptic power. This assists materially in 

 preserving the gelatine from putrefaction during the critical 

 period between extraction and concentration. 



REFERENCES. 



" Glue and Glue Testing," S. Rideal, D.Sc., 2nd ed., pp. 61-66, 78-82. 

 " Gelatine, Glue, and Allied Products," T. Lambert, pp. 29, 30, 49, 51. 

 " Chemical Engineering," /. R. San. Inst., No. 2, 1910. S. Rideal. 

 On adsorption phenomena : 



1. " Chemistry of Colloids," Dr. W. W. Taylor. 



2. " Chemistry of Colloids," V. Poschl. 



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



4. " Chemistry and Physics of Colloids," E. Halschek. 



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



