WOOL AND SILK BLEACHING 



241 



220. Commercial Bleaching. In commercial bleaching the 

 material to be bleached is first moistened with a very weak 

 solution of sulphuric acid or hydrochloric acid, and is then 

 immersed in the bleactiing powder solution. As the moist 

 material is drawn through the bleaching solution, the acid on 

 the fabric acts upon the solution and releases chlorine. The 

 chlorine thus set free immediately attacks the coloring matter 

 and destroys it, leaving the material in a bleached condition. 

 The bleached material is then immersed in a neutralizing 

 bath and is finally rinsed thoroughly in water. Strips of 

 cotton or linen many miles long are drawn by machinery into 

 and out of the various solutions (Fig. 159), are then passed 



FlG. 159. The material to be bleached is drawn through an acid a, then through a 

 bleaching solution b, and finally through a neutralizing solution c. 



over pressing rollers, and emerge snow white, ready to be 

 dyed or to be used as white fabric. . 



221. Wool and Silk Bleaching. Animal fibers like silk, wool, 

 and feathers, and some vegetable fibers like straw, cannot be 

 bleached by means of chlorine, because it attacks not only the 

 coloring matter but the fiber itself, and leaves it shrunken 

 and inferior. Cotton and linen fibers, apart from the small 

 amount of coloring matter present in them, contain nothing 

 but carbon, oxygen, and hydrogen, while animal fibers con- 

 tain in addition to these elements some compounds of nitro- 

 gen. The presence of these nitrogen compounds influences 

 the action of the chlorine and produces unsatisfactory results. 

 For animal fibers it is therefore necessary to discard chlorine 

 CL. GEN. sci. 1 6 



