226 SMITH'S INTERMEDIATE CHEMISTRY 



water without much alteration. But wool and silk contain com- 

 pounds of nitrogen (proteins) and are acted upon as rapidly as are 

 the traces of colored matter themselves. Hence sulphurous acid 

 (see p. 259) is used for bleaching these materials. 



Bleaching Powder as a Disinfectant. A disinfectant is a 



substance which destroys bacteria and other minute, and often 

 harmful organisms. Bleaching powder CaCl(OCl) has a distinct 

 odor. Tlusjte^hi^to the slow action of the carbon dioxide and 

 moisture of the air upon the salt, liberating hypochlorous acid. 

 Bleaching powder, when scattered around, will therefore dis- 

 infect the surrounding air, because the hypochlorous acid thus 

 liberated kills all bacteria present by oxidation. 



When an epidemic of typhoid fever occurs, it is usually traced 

 to the presence of colon bacilli and typhoid organisms in the drink- 

 ing water. The most effective means of destroying these bacilli is 

 to add, at the distributing point, a small proportion of bleaching 

 powder (about 20 pounds per million gallons of water). 



Recently, chlorine-water has in many cases taken the place of 

 bleaching powder for this purpose. Cylinders of liquid chlorine 

 (p. 144) were used in the Great War to kill germs as well as to 

 kill Germans, all water supplies being sterilized, whenever possible, 

 by the addition of very minute amounts of chlorine. 



Oxidations Previously Mentioned. The simplest oxida- 

 tions are reactions in which free oxygen is actually used up, for 

 example in the union of oxygen with metals and with non-metals : 



2Cu + O 2 -*2CuO. 

 S + O 2 -> SO 2 . 



The displacement of another element from a compound by 

 oxygen is also oxidation : 



4HC1 + O 2 5 2H 2 O + 2C1 2 . 



