Am  j*n.^&rm'}  Oxygen  and  its  Medicinal  Application.  13 
cussion.  Sift  several  times  through  a  moderately  fine  sieve,  and  dry 
in  a  moderately  heated  oven,  leaving  the  door  open.  It  is  essential 
that  pure  potassium  chlorate  and  manganese  dioxide  containing  no 
organic  matter,  be  used.  For  the  former,  the  writer  always  uses  the 
English  brands,  and  for  the  latter  the  Russian.  This  manganese 
dioxide  in  addition  to  being  purer  than  that  usually  found  in 
commerce,  presents  the  added  advantages  of  being  more  "  grainy  "  in 
character,  and  less  liable  to  fill  up  the  condensing  chamber.  As  to 
the  utility  of  precipitated  ferrous  carbonate  in  the  mixture,  that  is  an 
open  question.  It  is  claimed  that  it  absorbs  any  free  chlorine  gas 
generated,  converting  it  intf  ferric  chloride.  In  the  absence  of 
preservative  agents,  however,  ferrous  carbonate  is  rapidly  changed 
into  ferric  carbonate  on  exposure  to  air,  and  it  is  most  probable  that 
after  drying  this  change  ensues;  so  in  the  making  of  the  generating 
mixture  the  writer  has  left  out  that  compound,  and  his  results  have 
been  all  that  could  be  desired. 
To  generate  the  gas,  heat  the  horizontal  cylinder  or  retort,  at  the 
end  attached  to  the  central  support,  and  when  the  gas  from  the 
material  directly  over  it  is  exhausted,  move  the  lamp  or  burner  an 
inch  or  so  towards  the  other  end  of  the  retort.  Continue  until  the 
quantity  of  gas  desired  is  obtained.  The  rapidity  of  evolution  of 
gas  may  be  gauged  by  the  bubbling  of  gas  through  the  wash 
bottles ;  when  the  cylinder  is  exhausted  the  bubbling  will  abruptly 
cease.  A  freshly  filled  cylinder  must  be  used  each  time  the  gas  is 
generated.  If  the  contents  of  one  cylinder  do  not  yield  sufficient 
gas,  a  second  one  must  be  used.  After  applying  the  heat,  promptly 
remove  the  rubber  cork  from  the  bottom  of  the  posterior  upright 
tube  or  condenser,  or  there  may  be  sufficient  back-pressure  from 
partial  vacuum  to  cause  trouble. 
When  from  use  the  absorbent  cotton  in  the  fifth,  or  drying  bottle 
becomes  saturated  with  moisture,  it  should  be  removed  and  replaced 
with  dry.  The  retorts  are  cleaned  with  hot  water,  and  thoroughly 
dried  before  being  used  again.  In  filling  the  retorts  care  must  be 
taken  to  prevent  any  form  of  organic  matter,  such  as  paper,  wood  or 
cotton  fibre,  from  mixing  with  the  material ;  otherwise  an  explosion 
by  oxidation  may  result.  Renew  the  solutions  in  the  wash  bottles 
as  often  as  they  become  decomposed.  No  fixed  rule  can  be  given ; 
but,  in  general,  if  pure  chemicals  be  used,  after  300  to  500  gallons 
of  gas  have  been  generated.    The  gas  generated  can  be  retained  in 
