NITROGEN.  57


These  oxides  illustrate  well  the  great  law  of  multiple
proportions.  When  one  substance  unites  chemically  with
another,  it  is  in  some  definite  proportion,  or  multiple  of
that  proportion.  Whenever  substances  are  united  phys-
ically (mechanically,  as  in  alloys  of  metals,  etc.)  they
may  be  united  (mixed)  in  any  proportion.
NOTE.  —  We  see  from  the  above  that  there  is  a  third  class  of  indif-
ferent oxides  (as  N.,O2,  N2O4),  neither  acid-forming  nor  basic.  The
pupil  need  not  give  much  attention,  however,  to  this  class.  All  the
positive  indifferent  oxides,  as  Mn  O.2,  Ba  O2,  K2O4,  Pb  O2,  having
more  O  than  the  basic,  are  called  peroxides.  For  preparation  of
N2O3  and  N.2O5  see  larger  text  books.
EXP.  36.  —  Heat  in  flask  ammonium  nitrate  and  collect  gas  over  pneu-
matic tub  of  warm  water.
H4N  NO3    =     2  H2O    -|-    N2O

Hyponitrous  oxide  ("nitrous  oxide"  "laughing  gas,")
inhaled  with  a  small  proportion  of  O,  produces  a  peculiar
intoxication,  hence  its  name  of  "laughing  gas."  If  the
pure  gas  is  inhaled,  it  soon  produces  insensibility.  It  is
•  much  used  as  an  anaesthetic  by  dentists  and  by  surgeons
in  minor  operations.  It  is  kept  condensed  in  liquid  state
in  iron  cylinders.
EXP.  37.  —  To  small  pieces  of  copper  add  dilute  (25  per  cent.)  nitric
acid,  red  fumes  appear  in  generator  (see  EXP.  38),  but  a  colorless  gas
collects  over  the  tub.
_  /

Reaction  (irregular)  :  Cu3  +  8  H  N  O3  =  3  Cu  2  N  O3  -f-  4  H2  O  +  N2  O  2

[Filter  water  in  flask,  evaporate,  and  obtain  blue  crystals  of
'Cu8NO&].
EXP.  38.  —  Admit  to  test  tube  containing  N.2O2  a  bubble  of  O  (or
air).  Red  fumes  of  N.2  O4  appear.
