410 
NITRATE  OF  AMMONIA  AND  NITROUS  OXIDE. 
sold  with  a  ground-glass  stopper  ;  but  owing  to  the  variations  of 
temperature  to  which  the  retort  is  subjected,  it  causes  trouble 
by  being  too  loose  at  times,  and  difficult  of  removal  at  others.  A 
good  cork  is  to  be  preferred.  These  retorts  are  made  of  various 
shapes ;  that  which  seems  to  have  given  entire  satisfaction  is 
illustrated  in  the  cut  accompanying  this  article  (page  412.) 
The  solutions  recommended  for  washing  the  gas — caustic  pot- 
ash and  copperas — are  intended  to  neutralize  any  noxious  pro- 
ducts caused  by  the  use  of  impure  nitrate  of  ammonia,  or  by  an 
excess  of  heat  in  the  process.  The  caustic  potash  solution 
neutralizes  any  free  nitric  acid  which  may  distill  over.  The  cop- 
peras solution  destroys  either  chlorine  or  nitric  oxide — binoxide 
of  nitrogen.  The  sulphuric  acid  is  added  to  the  copperas  solu- 
tion to  prevent  precipitation  and  insure  a  clear  solution.  After 
having  passed  through  these  solutions,  it  should  not  be  inhaled 
immediately,  but  allowed  to  remain  for  two  or  three  hours  in  the 
receiver  over  the  water.  It  can  then  be  tested  by  breathing  it, 
and  if  it  has  not  a  coppery  taste,  and  does  not  produce  a  hot 
sensation  in  the  lungs,  it  may  be  relied  upon  as  pure  ;  but  if  it 
cannot  be  breathed  pleasantly,  it  should  be  allowed  to  remain  in 
the  gasometer  until  it  can.  When  pure  it  possesses  a  very  slight 
odor  and  a  sweetish  taste.  It  improves  by  age,  and  in  a  gasome. 
ter,  such  as  is  illustrated  on  a  subsequent  page,  may  be  kept  for 
many  weeks  ;  for  although  water  takes  up  from  5-  to  8-10ths  of 
its  own  bulk  of  the  gas,  after  it  is  once  saturated  it  will  not  take 
up  any  more,  except  as  the  water  will  gradually  give  out  the  gas 
and  take  up  air  through  the  surface  exposed  between  the  holder 
and  receiver.  It  has  been  suggested  that,  if  this  surface  were 
covered  with  a  thin  film  of  oil,  this  process  would  be  entirely 
prevented,  and  gas  thus  protected  has  been  said  to  have  been  re- 
tained in  the  gasometer  for  a  month. 
The  mouth-piece  or  inhaler  should  be  constructed  with  a  double 
valve,  preventing  the  exhalations  from  the  lungs  from  being 
thrown  back  into  the  gasometer  or  bag  from  which  the  gas  is 
administered. 
Some  operators  have  the  gasometer  placed  in  the  cellar  or  in 
a  room  adjoining  the  office,  and  connect  with  it  by  a  rubber 
tubing  passing  through  the  floor  or  partition,  thus  allowing  the 
