ON  ANTIMONIAL  VERMILION. 
339 
lower  part  of  the  vessel  projects  a  furnace-pipe  bent  at  right 
angles,  which  is  attached  to  a  small  clay  furnace.  Into  this 
furnace  sulphur  is  thrown  by  little  and  little,  and  burns  into 
sulphurous  acid,  which  passes  through  the  tube  into  the  vessel, 
and  there  acts  upon  the  carbonate  of  soda.  The  combustion  of 
the  sulphur  may  be  regulated  as  occasion  requires  through  the 
door  of  the  furnace  ;  the  draught  is  quite  sufficient,  and  in  the 
course  of  three  or  four  days  the  crystals  of  carbonate  of  soda  are 
acted  upon  to  a  considerable  depth.  The  very  friable  sulphite 
of  soda  may  be  readily  separated  from  the  unaltered  nucleus  if 
any  remains,  and  the  latter  may  then  be  put  back  into  the  sieve. 
The  sulphite  of  soda  is  dissolved  in  water  so  as  to  produce  a 
solution  of  25°  B.,  and  this  is  saturated  whilst  hot  with  crystal- 
lized carbonate  of  soda.  When  effervescence  no  longer  occurs 
on  the  addition  of  this  salt  (which  is  the  best  criterion,  as  litmus- 
paper  gives  no  satisfactory  indications),  or  rather  when  the  dilute 
sulphite  furnishes  a  slight  effervescence  of  carbonic  acid  on  the 
addition  of  muriatic  acid,  flowers  of  sulphur  are  added,  and  the 
mixture  is  heated  in  an  earthen  vessel  for  three  hours  on  the 
water-bath,  stirring,  and  replacing  the  water  that  evaporates. 
When  the  fluid  is  cool,  it  is  filtered  and  diluted  until  it  shows 
25°  B. 
Perchloride  of  antimony  is  prepared  by  heating  powdered  black 
sulphuret  of  antimony  with  commercial  muriatic  acid.  When 
the  evolution  of  sulphuretted  hydrogen  begins  to  diminish  at  a 
gentle  heat,  the  mixture  is  boiled  for  a  few  minutes.  On  cooling, 
the  clear  liquid  is  decanted.  To  avoid  inconvenience  from  the 
sulphuretted  hydrogen  gas  evolved  during  the  solution  of  the 
sulphuret  of  antimony,  it  may  either  be  passed  into  a  solution  of 
soda,  or  allowed  to  pass  through  a  tube  drawn  out  to  a  point  at 
the  extremity,  close  to  which  the  flame  of  a  spirit-lamp  is  placed  ; 
by  this  the  sulphuretted  hydrogen  is  burnt,  even  when  it  is 
mixed  with  much  aqueous  vapor.  The  solution  of  chloride  of 
antimony  obtained  is  diluted  with  water  to  25°  B. 
When  the  solutions  of  hyposulphite  of  soda  and  chloride  of 
antimony  are  thus  prepared,  the  antimonial  vermilion  is  prepared 
in  the  following  manner : — 4  litres  of  solution  of  chloride  of 
antimony  and  6  litres  of  water  are  poured  into  a  stoneware  basin, 
and  after  these  10  litres  of  the  solution  of  hyposulphite  of  soda. 
