SULFUR AND ITS COMPOUNDS 99 



Is it a chemically active substance ? (6) Why does it act as a 

 bleaching agent ? (7) Why is it valuable as a disinfectant ? 



117. Sulfuric Acid. Sulf uric acid can not be produced 

 from sulfates as HC1 and HNO 3 were produced from their 

 salts, because there is no acid or other material that can 

 be used economically for the purpose. H 2 SO 4 is made 

 from its elements by the use of an oxidizing agent. The 

 different steps in its production are : 



(1) Burning of sulfur, or roasting of some ore, as 

 pyrites, which contains sulfur. The S forms with O, SO 2 . 



(2) Union of SO 2 and H 2 O, forming sulfurous acid, 

 H 2 SO 8 . 



(3) Oxidation of H 2 SO 3 to form H 2 SO 4 . This is accom- 

 plished by the use of NO 2 reduced to NO, which in turn 

 is capable of uniting with the oxygen of the air, re- 

 forming NO 2 . NO is used as a carrier of O ; hence the 

 oxygen of the air is used indirectly for the oxidation 

 of H 2 SO 3 . The different reactions take place simulta- 

 neously in lead-lined chambers : 



SO 2 -f H 2 O -|- N0 2 = H 2 SO 4 + NO. 



NO + O = N0 2 . 

 Other and more complicated reactions also take place. 



The crude acid is then concentrated and purified. Sul- 

 furic acid is extensively used in industrial operations. 

 There is scarcely a chemical product in the preparation of 

 which H 2 SO 4 has not been used either directly or in- 

 directly. H 2 SO 4 takes an important part in the manufac- 

 ture of soda, which, in turn, is used for making glass ; in 

 the preparation of commercial fertilizers, and of many 

 food products. The amount of sulfuric acid which a 



