BLEACHING POWDER 239 



ganese itself combines with part of the chlorine originally 

 in the acid; but not with all. There is thus some free chlo- 

 rine left over from the acid, and this passes off as a gas 

 and can be collected, as in Figure 158. Free chlorine is 

 heavier than air, and hence when it leaves the exit tube it 

 settles at the bottom of the jar, displacing the air, and finally 

 filling the bottle. 



Chlorine is a very active substance and combines readily 

 with most substances, but especially with hydrogen ; if 

 chlorine comes in contact with steam, it abstracts the hydro- 

 gen and unites with it to form hydrochloric acid, but it leaves 

 the oxygen free and uncombined. This tendency of chlorine 

 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 

 the 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 destroys it. 



Chlorine has no effect on dry material, as may be seen if 

 we put dry gingham into the jar; in this case there is no 

 water to furnish hydrogen for combination with the chlorine, 

 and no oxygen to be set free. 



219. Bleaching Powder. Chlorine gas has a very injurious 

 effect on the human body, and hence cannot be used directly 

 as a bleaching agent. It attacks the mucous membrane 

 of the nose and lungs, and produces the effect of a severe 

 cold or catarrh, and when inhaled, causes death. But certain 

 compounds of chlorine are harmless, and can be used instead 

 of chlorine for destroying either natural or artificial dyes. 



