224 SMITH'S INTERMEDIATE CHEMISTRY 



Used as a disinfectant (see p. 226), it oxidizes and destroys bac- 

 teria. Hypochlorous acid is more energetic as an oxidizing agent 

 than is ozone or hydrogen peroxide, and is used extensively in 

 bleaching. 



Chlorine-Water. It will be recalled that chlorine acts chemic- 

 ally upon water (p. 145) : 



C1 2 + H 2 O <=> HC1 + HOC1 



giving hydrochloric acid and hypochlorous acid. The action is 

 reversible (read the equation backwards), and in half -saturated 

 chlorine solution about one-third only of the chlorine has under- 

 gone the change shown in the equation. But, if a substance 

 which can be oxidized, such as a dye (attached, perhaps, to cloth), 

 is introduced into the solution, the HOC1 which is present transfers 

 its oxygen to the dye-stuff. This leaves HC1 alone in the solution, 

 and stops the backward reaction. Hence more of the chlorine 

 acts upon the water, and more hypochlorous acid is formed. This, 

 in turn, is used up. Thus, in a few moments, all the 

 free chlorine is gone, only dilute hydrochloric acid 

 remains, and a colorless organic compound is left 

 on the cloth or in the solution. 



Chlorine itself is often, erroneously, spoken of as 

 the bleaching agent. If a dry, colored cloth be 

 hung for a week in chlorine, dried by having sul- 

 phuric acid in the bottle (Fig. 65), little or no 

 change in color will occur. But a wet rag is bleached 

 as soon as the chlorine has time to dissolve in the 

 FIG. 65 water, and give the necessary hypochlorous acid. 



Bleaching Powder. CaCl(OCl) is made by the action of 

 chlorine on slaked lime: 



Ca(OH) 2 + Cli -> CaCl(OCl) + H 2 O. 



The action is not complete in practice, and the resultant product 

 is always a basic salt. In solution it gives the ions Ca++, Cl~, and 



