536 
PROCESS  FOR  PREPARING  JAMES'  POWDER. 
current  of  air  to  pass  through.  The  skittle-pot  and  its  contents 
will  thus  be  brought  to  a  uniform  bright  red-heat,  which  may  be 
maintained  at  that  degree  for  about  an  hour,  more  or  less,  ac- 
cording to  the  quantity.  The  skittle-pot  is  then  to  be  taken 
from  the  fire,  and  should  the  powder  prove  to  be  pure  white, 
except  perhaps  a  thin  layer  at  the  top,  it  only  requires  to  be  re- 
duced to  the  finest  powder  in  an  earthen  mortar,  and  sifted 
through  a  fine  silk  sieve.  Should  the  powder  not  prove  white, 
it  may  be  returned  to  the  skittle-pot,  placed  in  the  fire  as  before, 
and  continued  in  a  state  of  ignition  for  half  an  Jiour,  according 
to  the  judgment  of  the  operator. 
In  the  first  part  of  the  process,  the  sulphuret  of  antimony  is 
slowly  decomposed ;  its  sulphur  burns,  and  exhales  in  the  state 
of  sulphurous  acid.  The  antimony,  now  insulated,  appears  in 
small  brilliant  spiculse,  which,  as  the  heat  increases,  gradually 
disappear.  In  the  second  part  of  the  process,  when  the  roasted 
matter  is  heated  in  the  skittle-pot,  the  antimony,  while  in  the 
state  of  vapor,  combines  with  oxygen,  and  is  converted  into  pro- 
toxide, part  of  which  crystallizes  in  the  upper  part  of  the  skittle- 
pot,  or  escapes  as  a  thick,  white  smoke.  The  heat  increasing, 
the  protoxide  is  converted  into  antimoniate  of  antimony,  which 
remains  mixed  or  combined  with  the  phosphate  of  lime. 
If  the  heat  be  raised  much  above  that  of  a  good  coal  fire  in  a 
common  grate,  the  mass  will  slightly  cohere,  and  in  some  parts 
will  become  yellowish  and  vitreous.  If  the  heat  be  still  higher, 
as  that  of  an  air-furnace,  the  powder  will  change  to  an  olive- 
brown  mass  as  hard  as  stone. 
All  the  time  the  powder  is  in  the  skittle-pot  and  very  hot, 
protoxide  of  antimony  is  escaping  or  crystallizing  on  the  cover, 
and  hence  the  diff'erence  discoverable  by  analysis,  and  by  the 
medical  effects  of  different  parcels  of  James's  powder.  It  there- 
fore becomes  an  important  and  difficult  question,  what  is  the 
criterion  by  which  the  completion  of  the  process  is  to  be  judged  ? 
I  know  of  no  other  than  this,  that  when  the  powder  is  white  it 
is  fit  for  use  ;  any  greater  or  longer-continued  heat,  I  believe  to 
be  injurious.  It  may  not  always  happen  that  the  whole  charge 
will  prove  white ;  when  it  does  not,  the  whitest  parts  are  to  be 
separated,  and,  if  worth  the  trouble,  the  remainder  may  be 
