266 SMITH'S INTERMEDIATE CHEMISTRY 



sulphur dioxide and water to form sulphurous acid is rapid, but the 

 action of free oxygen upon the latter, 2H 2 S0 3 4- 2 > 2H 2 S0 4 , is 

 exceedingly slow. Reaching sulphuric acid by the use of these two 

 changes, although they constitute a direct route to the result, is 

 not feasible in practice. On the other hand, both of the above 

 actions, (1) and (2), happen to be much more speedy, and so, by 

 their use, more rapid production of the desired substance is secured 

 at the expense of a slight complexity. 



The progress of the first action is marked by the disappearance 

 of the brown nitrous anhydride and, on the introduction of water, 

 the completion of the second stage results in the reproduction of 

 the same substance. The nitrous anhydride takes part a large 

 number of times in these changes, and so facilitates the conversion 

 of a great amount of sulphur dioxide, oxygen, and water into sul- 

 phuric acid, without much diminution of its quantity. Some 

 is unavoidably lost, however. 



The loss of nitrous anhydride is made good by the introduction 

 of nitric acid vapor into the chamber. This acid is made from con- 

 centrated sulphuric acid and commercial sodium nitrate NaNO 3 : 



NaN0 3 + H 2 S0 4 * HN0 3 T + NaHS0 4 . 



On account of the volatility of the nitric acid, a moderate heat is 

 sufficient to remove it from admixture with the other substances, 

 and its vapor is swept along with the other gases into the appara- 

 tus. The first reaction which this vapor undergoes may be 

 written : 



H 2 + 2S0 2 + 2HN0 3 -> 2H 2 SO 4 + N 2 O 3 . 



Details of the Chamber Process. The sulphur dioxide is 

 produced in a row of furnaces A (Fig. 71). The gases from the 

 various furnaces pass into one long dust-flue, in which they are 

 mingled with the proper proportion of air, and deposit oxides of 

 iron and of arsenic, and other materials which they transport 

 mechanically. From this flue they enter the Glover tower G, 

 in which they acquire the oxides of nitrogen. Having secured 





