^  394  Analysis  of  Graphite.  {nipZ-.f,';""'- 
from  water,  in  an  incandescent  state,  to  the  air,  will  probably  present 
itself  to  the  mind  at  first  glance.  Practice,  however,  does  not  confirm 
this  ;  as  even  small  particles  of  graphite,  after  being  exposed  for  sev- 
eral days  in  a  crucible  to  the  action  of  a  high  heat,  are  not  entirely 
consumed. 
Although  the  elementary  analysis  performed  either  with  CuO,  finally 
in  a  current  of  O,  or  with  PbCrO^,  meets  all  that  is  required  in  this 
respect,  nevertheless  the  method  which  Berthier  recommends  for  deter- 
mining the  combustion  value  of  a  substance  is  far  preferable,  as  being 
simpler,  more  convenient,  and  technically  accurate  enough. 
Triturate  in  an  agate  mortar  i  gram  graphite,  as  fine  as  possible,  with 
25  grams  finely-powdered  litharge  introduce  the  mixture  into  an 
unglazed,  tapering  porcelain  crucible  ;  cover  it  with  25  grams  more 
PbO,  attach  the  lid,  and  expose  to  a  slow  heat  on  coal,  when,  after 
some  foaming  and  effervescing,  complete  fusion  will  be  attained  in 
about  ten  to  fifteen  minutes.  The  reduced  lead  is  united  to  a  single 
lump  at  the  bottom  of  the  crucible,  and  may,  after  cooling,  be  readily 
separated  with  a  hammer  from  the  sides  of  the  crucible  and  the  adher- 
mg  litharge.    34  parts  reduced  lead  are  equivalent  to  i  part  of  carbon. 
Frequently  it  is  found  necessary  to  determine  quantitively  the  other 
constituents  of  graphite  besides  carbon.  To  achieve  this  result  by  a 
single  analysis,  avoiding  the  above-described  treatment  with  lead,  I  have 
used  the  following  process  with  good  success  :  i  gram  of  finely-pulve- 
rized graphite  is  heated  to  a  dull-red  heat,  the  loss  thereby  sustained 
being  calculated  as  water ;  then  triturate  intimately  with  3  grams  of  a 
mixture  of  equal  parts  of  carbonate  of  potassium  and  of  sodium  :  intro- 
duce the  whole  into  a  platinum  crucible,  cover  with  i  gram  of  potas- 
sium hydrate  or  sodium  hydrate,  and  gradually  heat  to  incandescence  ; 
the  mass  thereby  melts,  foams,  and  forms  a  crust  on  top,  which  is 
occasionally  pressed  down  with  a  strong  platinum  wire.  After  fusing 
for  half  an  hour,  allow  to  cool ;  soften  the  mass  with  water,  and  heat 
for  fifteen  minutes  nearly  to  boiling  ;  filter,  lixiviate,  and  set  the  entire 
liquid  aside. 
1  he  object  of  fusing  with  the  alkalies  is  to  entirely  separate  the 
admixtures  insoluble  in  acids,  as  clay  and  quartz.    Whether  by  this 
*  As  commercial  litharge  sometimes  contains  metallic  lead,  it  should  be  tested 
for  it  by  treating  it  with  acetic  acid,  whereby  the  metal  remains.  In  case  such  im- 
purity occurs,  and  no  pure  PbO  is  at  hand.  It  Is  necessary  to  determine  the  amount 
of  lead  and  deduct  It  from  the  result  obtained  In  the  manipulation. 
