OXIDIZING SUBSTANCES 221 



not affected by ordinary oxygen. Thus, it rusts silver to black 

 silver peroxide Ag 2 2 . 



2Ag + 20 3 -> A&Oj, + 20 2 . 



Ozone also oxidizes a number of organic compounds which are 

 unchanged in atmospheric oxygen. For example, when ozon- 

 ized oxygen is bubbled through a dilute indigo solution, a yellow 

 substance, of much paler tint, isatin, is formed, and the indigo is 

 said to have been bleached. Indigo is taken, for illustration, 

 because it is a most widely used dye, employed in dying navy-blue 

 and blue-black goods, and is totally unaffected by light, and by 

 oxygen, soap, and other ordinary substances: 



Ci 6 H 10 N 2 2 + 20 3 - 20 2 + 2C 8 H 5 N0 2 . 



indigo isatin 



Litmus, and the traces of coloring matter in wax, starch, flour, 

 and ivory are all oxidized by ozone to colorless, or nearly colorless, 

 substances. For this reason it is used commercially in bleaching 

 the last-named materials. 



Ozone is sometimes recommended for use, in connection with 

 ventilation, as a means of destroying minute organisms in the air. 

 Recent investigations have shown, however, conclusively, that 

 when thus diluted with air, it has little value as a germicide. It 

 is employedjbx^some_ cities for sterilizing the water supply. 



HYDROGEN PEROXIDE 

 Preparation. Sodium peroxide Na 2 O 2 , produced by burning 

 sodium in dry air, can be dissolved, a little at a time, in ice-cold 

 water. When this solution is acidified with hydrochloric or sul- 

 phuric acid, a double decomposition takes place: 

 2HC1 -4 2NaCl + H 2 O 2 



and a dilute solution of hydrogen peroxide (mixed with common 

 salt) is obtained. The nature of the action shows the product to 

 be an acid, with the negative radical O 2 n . 



