360      SPIRIT  OF  NITROUS  ETHER  AND  NITRITE  OF  SODA. 
soda  without  allowing  deflagration  to  take  place  at  all,  and  this 
at  times  has  been  very  successfully  performed ;  but  it  has  this 
great  drawback,  that  despite  all  the  caution  employed,  the  mixture 
is  always  liable  to  burst  suddenly  into  deflagration  and  even 
comparative  explosion. 
It  was  next  tried  to  substitute  a  harder  form  of  carbon  for  the 
purpose,  and  finely  powdered  plumbago  was  selected  ;  this  is 
somewhat  more  manageable  and  under  control,  and  has  answered 
the  purpose  better.  Several  hundred  pounds  weight  of  salt,  con- 
taining about  75  per  cent,  of  nitrite  of  soda,  have  been  manufac- 
tured by  this  means  ;  still  at  times  we  have  had  sudden  bursts 
of  deflagration,  and  this  makes  the  men  nervous,  from  its  oc- 
curring when  they  were  off  their  guard,  and  burning  their  clothes 
or  skin. 
My  next  experiment  was  to  substitute  for  the  charcoal  an 
equivalent  amount  of  carbon  in  the  form  of  starch,  and  this  has 
yielded  us  the  most  satisfactory  results,  and  with  very  little 
trouble.  Seven  parts  of  dried  nitrate  of  soda  in  fine  powder  is 
mixed  with  one  of  starch  powder,  and  thrown  by  small  quanti- 
ties at  a  time  into  a  shallow  iron  pan  heated  from  below  ;  the  mix- 
ture spumes  and  melts  as  the  water  and  carbonic  acid  pass  off, 
and  the  salt  ultimately  fuses.  When  it  has  become  quite  white, 
it  is  laded  out  and  cooled.  We  have  already  made  between 
three  and  four  hundred  pounds  weight  by  this  process,  and  with- 
out any  annoyance  from  deflagration,  the  heat  of  course  being 
carefully  regulated.  In  these  operations  we  have  always  employed 
iroh  vessels,  as  the  metal  vessel  relieves  us  from  the  annoyance 
of  loss  arising  from  leakage  or  fracture  of  the  earthen  crucible, 
and  the  small  quantity  of  oxide  of  iron  that  is  found  mixed  with 
the  product  cannot  in  any  way  interfere  with  the  after  process. 
The  spirit  of  nitre  that  has  been  produced  from  nitrite  of  soda 
thus  prepared  has  yielded  us,  by  the  chloride  of  calcium  test,  5 
per  cent,  of  separated  nitrous  ether,  or  13  per  cent,  as  a  whole ; 
and  in  consequence  of  this  steady  yield,  we  have  been  obliged 
to  reduce  the  proportion  of  nitrite  used  in  our  manufacture  to 
meet  this  excess  of  strength  ;  the  British  Pharmacopoeia  ruling 
that  the  spirit  is  to  yield  1J  per  cent,  of  nitrous  ether  when  sub- 
mitted to  the  test,  or  a  total  content  of  9*5  per  cent. 
