PERMANGANATE  OF  POTASH  AS  AN  OXIDIZING  AGENT.  79 
into  sulphuric  acid,  which  is  then  precipitated  by  a  soluble  salt 
of  baryta.  Nitric  acid  is  usually  employed  for  the  oxidation  of 
the  sulphur,  but  its  action  is  slow  and  difficult.  It  only  be- 
comes complete  by  long  boiling  with  concentrated  nitric  acid, 
and  in  operating  upon  sulphuretted  organic  matters,  we  have  to 
fear  either  an  imperfect  oxidation  or  a  loss  of  sulphuric  acid  by 
volatilization.  The  action  of  nitric  acid  is  therefore  often  re- 
placed by  that  of  a  mixture  of  nitrate  of  potash  and  an  alka- 
line carbonate  in  fusion,  into  which  the  matter  to  be  analysed  is 
thrown  in  small  portions.  This  process  is  inconvenient  in  ope- 
rating upon  gunpowder,  which  must  be  mixed  with  several  times 
its  weight  of  chloride  of  sodium,  in  order  to  moderate  the  re- 
action. 
The  authors  propose  to  effect  the  conversion  of  sulphur  into 
sulphuric  acid  by  means  of  permanganate  of  potash.  For  this 
purpose  crystallized  permanganate,  containing  no  appreciable 
traces  of  sulphate,  must  be  employed.  To  ascertain  that  the 
salt  contains  no  sulphate  of  potash,  a  small  quantity  may  be 
boiled  with  pure  muriatic  acid  until  it  is  completely  decomposed  ; 
the  liquid  should  not  precipitate  chloride  of  barium. 
The  operation  is  performed  as  follows,  taking  gunpowder  as 
an  example  of  the  material  to  be  analysed  : — About  1  grm0  of 
powder  is  weighed  very  accurately,  and  dried  in  a  stove  or  a 
current  of  dry  air  at  112°  F.  until  it  no  longer  loses  its  weight, ; 
in  this  way  the  quantity  of  water  is  determined.  The  dried 
material  is  then  put  into  a  small  glass  matrass  with  a  saturated 
solution  of  permanganate  of  potash  ;  and  the  liquid  is  boiled, 
with  the  addition  of  permanganate  from  time  to  time,  until  the 
mixture  has  a  persistent  violet  tint. 
All  the  sulphur  in  the  powder  is  then  converted  into  sulphu- 
ric acid,  and  the  carbon  into  carbonic  acid  ;  the  liquid  holds 
oxide  of  manganese  in  suspension  ;  concentrated  muriatic  acid 
is  added,  and  the  whole  is  boiled  until  the  oxide  is  completely 
dissolved,  which  only  requires  a  few  minutes.  If  the  solution 
of  the  oxide  be  slow,  the  liquid  is  too  dilute,  and  must  be  con- 
centrated by  evaporation  ;  after  which  pure  muriatic  acid  is 
again  added  ;  a  slight  excess  of  chloride  of  barium  is  then  poured 
into  the  balloon,  so  as  to  precipitate  all  the  sulphuric  acid,  a  lit- 
tle nitric  acid  is  added,  and  the  whole  is  boiled  so  as  to  give  co- 
