XITEOGEX AXD ITS OXIDES. 



Some acids contain two or more atoms of hydrogen, which may be re- 

 placed successively by a metal ; if only one atom of hydrogen is thus 

 exchanged, an acid salt is formed ; if both atoms of hydrogen are ex- 

 changed for two atoms of a monad or one atom of a dyad metal (see 44), 

 a neutral salt results. You will observe this in the study of sulphuric 

 acid. 



81. Nitrous Oxide, or Laughing-Gas. This gas is the com- 

 pound of oxygen and nitrogen, which has the smallest pro- 

 portion of oxygen. It is obtained by heating ammonium 

 nitrate in a re- 

 tort or flask, 

 a. Complete 

 decomposition 

 ensues; the gas 

 is washed in 

 the flask, b, and 

 collected in 

 the receiver, c. 

 "We obtain two 

 substances en- 

 tirely different 

 from each oth- 



Fig. 14. 



er and from the substance from which they come, viz., water 

 and the nitrous oxide gas : 



Ammonium nitrate. 

 NH 4 N0 3 



Nitrous oxide. 

 N S O 



Water. 



The vapor of the water and the gas pass together into the 

 second flask ; but there the vapor is condensed into water, 

 and the gas bubbles up into the glass jar set in the trough 

 to receive it. Some caution is necessary in preparing this 

 gas, or it may be impure, and therefore injurious to those 

 who may inhale it. To avoid this the material must be 

 pure, the heat must not be so great as to cause fumes to 

 rise in the retort, and the gas should be passed through 



