NITRIC ACID 315 



This gas is used as a catalytic agent in the chamber process (p. 

 264) for making sulphuric acid. The acid and its anhydride are 

 employed in the manufacture of many dyes. 



r Nitrous Oxide N 2 oV When ammonium nitrate, a white salt, 

 is~"h"eated, it decomposes into steam and nitrous oxide: 



NH 4 NO 3 -* 2H 2 t + N 2 O | . 



Nitrous oxide is somewhat more easily liquefied (b.-p. 90) than 

 is carbon dioxide. At 12 its vapor pressure is 41 atmospheres. 

 It is sold, as a liquid, in steel cylinders, and used as an anaesthetic 

 for minor operations, chiefly in dentistry. The hysterical symp- 

 toms which accompany its use caused it to be named "laughing 

 gas." 



Like oxygen, it relights a glowing splinter of wood, and supports 

 combustion brilliantly. It does not interact with nitric oxide (p. 

 311), as does oxygen, however, to form nitrogen tetroxide: 



The Writing of Equations. The reader will have discovered 

 that some of the equations in the present chapter are rather harder 

 than usual to balance correctly, even when the products of the 

 reaction are all known. The following sections should be read 

 through carefully, in order to obtain a thorough understanding 

 of the points under discussion. The hints given will be found of 

 general assistance in writing difficult equations. 



Points About Oxygen Acids. In dealing with an acid that 

 contains oxygen, like nitric acid, there are some things which we 

 must acquire the habit of keeping in mind. 



Thus, an oxygen acid, as we have seen (p. 257), can be deprived 

 of water, leaving the anhydride. The chemist always thinks of 

 the one as soon as the other is mentioned. If the acid is named, 

 he instantly subtracts water from its formula to get the formula 

 of the anhydride : 



Skeleton: HOC1-H 2 O 



