ON  CRYSTALLIZED  HYDRATE  OF  BARYTES.  129 
ON  CRYSTALLIZED  HYDRATE  OF  BARYTES. 
By  Frederic  Mohr,  Ph.  D.,  Coblentz, 
Honorary  Member  of  the  Pharmaceutical  Society  of  Great  Britain. 
Caustic  barytes  has  been  hitherto  prepared  by  calcination  of 
nitrate  of  barytes,  or  by  boiling  a  solution  of  sulphuret  of  barytes 
with  oxide  of  copper.  The  first  process  has  been  improved  by 
me,  by  mixing  the  nitrate  of  barytes  with  coarsely  powdered 
native  sulphate  of  barytes,  and  heating  the  mixture  in  a  cruci- 
ble. By  this  simple  manipulation  the  rising  and  overflowing  of 
the  fused  salt  has  been  entirely  prevented.  It  has  constituted 
until  now  the  most  expeditious  and  the  cheapest  process  for  pre- 
paring the  crystals  of  hydrate  of  barytes. 
The  new  process,  for  the  first  time  here  to  be  published,  con- 
sists in  precipitating  caustic  barytes  by  a  solution  of  caustic 
potash  or  soda.  The  caustic  soda  is  prepared  from  a  pure  car- 
bonate of  soda  and  caustic  lime  by  the  common  method  of  boil- 
ing them  together  in  a  cast-iron  vessel,  until  a  filtered  portion 
shows  no  more  traces  of  carbonate  of  soda.  The  warm  liquid  is 
left  covered  for  sedimentation,  and  after  some  hours'  time  the 
perfectly  clear  liquid  is  taken  off  by  a  glass  syphon. 
This  is  the  solution  of  caustic  soda  to  be  used  for  preparing 
caustic  barytes.  To  ascertain  the  quantity  of  any  salt  of  barytes 
which  can  be  decomposed  by  caustic  soda,  the  alkalimetric  strength 
of  the  soda  must  be  previously  determined.  For  this  purpose 
ten  cubic  centimetres  are  taken  off  by  a  pipette,  some  drops  of 
tincture  of  litmus  are  added,  and  then  the  strength  is  determined 
by  a  solution  of  oxalic  acid  of  a  certain  and  known  strength, 
which  is  added  until  the  color  is  changed  to  red.  The  strength 
of  the  solution  of  oxalic  acid  is  prepared  in  the  way  originally 
suggested  by  Mr.  J.  J.  Griffin,  and  recommended  in  my  book 
Die  Titricmethode,  for  volumetrical  analysis.  A  litre  of  the 
solution  contains  sixty-three  grammes  of  crystallized  oxalic  acid, 
thus  representing  the  atomic  weight  of  the  acid.  A  cubic  cen- 
timetre of  this  solution  is  therefore  equal  to  the  one-thousandth 
atom  of  any  alkali.  Supposing,  then,  that  eight  cubic  centimetres 
of  this  solution  were  required  to  redden  the  litmus  in  ten  cubic 
centimetres  of  the  caustic  soda,  800  cubic  centimetres  of  the  latter 
would  decompose  one  atom  of  any  salt  of  barytes.    Ten  cubic 
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