CHLORINE, BROMINE, IODINE, AND FLUORINE. 163 



first step in the process is the decomposition of water, and 

 hence the necessity for having the substance to be bleached 

 moist. If a colored rag be introduced into chlorine gas dry, 

 the chlorine will have no effect upon it; but if it be moist- 

 ened, it will lose its color. The explanation of bleaching is 

 this : The chlorine, taking the hydrogen of the water, sets 

 free oxygen, and this in its nascent state ( 42) has special 

 chemical power, and attacks the coloring matter, destroy- 

 ing it, or burning it up, as we may say, for the union of 

 oxygen with other elements is, as you have seen, essential- 

 ly a combustion. It is oxygen, then, that really does the 

 bleaching here, just as in the case of sun-bleaching ( 196). 

 But the question arises, Why does the oxygen burn up the 

 coloring matter, and not the cloth itself? This is from a 

 principle which is well established in chemistry, viz., that 

 the more ingredients there are in a compound the more 

 easily it is decomposed. While the vegetable tissue or sub- 

 stance is composed of three elements, carbon, oxygen, and 

 hydrogen, the coloring matter is composed of these with ni- 

 trogen in addition, and therefore is more readily demolished 

 by the oxygen than the cloth is. 



217. Carrying the Bleaching too Far. But sometimes 

 the cloth is somewhat burned in the process that is, some 

 of the tissue is destroyed by the released oxygen, and the 

 cloth consequently weakened. This is done whenever, after 

 the chlorine has released sufficient oxygen to destroy the 

 coloring matter, it continues to release more. The point, 

 then, to be aimed at by the bleacher is to set free only just 

 enough oxygen by means of the chlorine to oxidize the col- 

 oring matter, and not the substance. There is the same 

 danger that the process may be carried too far in the com- 

 mon sun -bleaching, or grass -bleaching, as it is usually 

 called. 



218. Comparison with Grass-Bleaching. The old mode 



