SULPHUR. 179 



oxygen, is no longer nitric acid, but nitric oxide ; this imme- 

 diately absorbs oxygen from the air in the leaden chamber, 

 becoming nitric peroxide. Then this nitric peroxide, meet- 

 ing sulphurous anhydride, again gives up its oxygen; and 

 this process is repeated over and over. Thus you see the 

 nitric peroxide answers simply as a medium for delivering 

 over to the sulphurous anhydride the oxygen from the air. 



Fig. 79. 



The sulphuric acid that is formed becomes dissolved as 

 fast as it is made in the water in the lead chamber. In order 

 to facilitate this solution steam is constantly admitted into 

 the chamber, so that each particle of the acid may be dis- 

 solved as soon as it is formed. The water is in this way 

 sent in search of the acid. 



243. Explanation in Formulae. There are three stages : 



!Sr *. water. SU 'P!T C *** 



annjduue. acid. oxide. 



(1) 3(S0 3 ) + 2(HN0 3 ) + 2(H 3 0) = 3(H 3 SOJ + 2(NO) 



Nitric oxide. Oxygen. Nitric peroxide. 



(2) NO + O N0 3 



Nitric Sulphurous w Sulphuric Nitric 



peroxide. anhydride. acid. oxide. 



(3) N0 3 + SO a -f H 3 O = H 3 S0 4 + NO 

 then (2) is repeated, (3) follows, and so on. 



244. Properties. Sulphuric acid is the most powerful of 

 all the acids, and is therefore one of the most important 



