HOW CHLORINE BLEACHES 159 



An artificial bleaching agent. While the sun's rays are 

 effective as a bleaching agent, the process is slow; moreover, 

 it would be impossible to expose to the sun's rays the vast 

 quantity of fabrics used in the civilized world of to-day. 

 The huge and numerous bolts of material which daily come 

 from our looms and factories must therefore be whitened by 

 artificial means. The substance almost universally used as a 

 rapid artificial bleaching agent is chlorine, best known to us as a 

 constituent of common salt. Chlorine is never free in nature, 

 but is found in combination with other substances, as, for 

 example, in combination with sodium in salt, or with hydrogen 

 in hydrochloric acid. 



Free chlorine is obtained by pouring hydrochloric acid over 

 potassium permanganate crystals and gently heating the mix- 

 ture. The gas which forms is chlorine. 



How chlorine bleaches. Chlorine is an active substance and 

 combines readily with most substances, but especially with hy- 

 drogen. If chlorine comes in contact with steam, it abstracts the 

 hydrogen and unites with it to form hydrochloric acid, but it 

 leaves the oxygen free and uncombined. This tendency of chlo- 

 rine to combine with hydrogen makes it valuable as a bleaching 

 agent. In order to test the efficiency of chlorine as a bleach- 

 ing agent, drop a wet piece of colored gingham or calico into 

 a bottle of chlorine, and notice the rapid disappearance of 

 color from the sample. If unbleached muslin is used, the 

 moist strip loses its natural yellowish hue and becomes a 

 clear, pure white. The explanation of the bleaching power 

 of chlorine is that the chlorine combines with the hydrogen 

 of the water and sets oxygen free ; the uncombined free 

 oxygen oxidizes the coloring matter in the cloth and de- 

 stroys it. 



Chlorine has no effect on dry material, as is seen when we 

 put dry gingham into the jar; this is because there is no water 



