rochleder's  proximate  analysis. 
565 
treatment  with  baryta  iu  the  heat.  If,  by  heating  with  baryta,  instead  of 
a  clear  solution  a  solid  compound  is  obtained,  which  is  suspended  in  the 
fluidor  isdeposited  therein,  itis  separated  generally,  as  above  described  by 
filtration  from  the  fluid  after  the  addition  of  alcohol.  When  the  contents 
of  the  flask  have  been  treated  with  an  excess  of  sulphuric  acid  instead  of 
carbonic  acid,  and  then  filtered,  sulphate  of  baryta  is  found  on  the  filter, 
and  sometimes  a  decomposition  product,  insoluble  in  water,  mixed  with 
the  sulphate  of  baryta,  and  in  the  filtrate  a  little  free  sulphuric  acid,  and 
either  both  or  one  of  the  decomposition  products  dissolved  therein.  By  the 
careful  addition  of  baryta  water  the  sulphuric  aeid  is  separated.  The  fluid 
freed  from  sulphuric  acid  is  heated  in  a  distillatory  vessel,  and  the  distil- 
late examined  for  a  volatile  acid,  perchance  resulting  from  the  decomposi- 
tion of  the  original  substance.  The  residue  of  the  distillation  is  further 
examined  by  mixing  a  portion  thereof  with  perchloride  of  tin,  sugar  of  lead, 
subacetate  of  lead,  and  baryta  water.  It  generally  happens  that  one  of 
the  decomposition  products  is  thrown  down  in  the  form  of  an  insoluble 
compound  by  one  of  these  precipitants,  while  the  other  decomposition  pro- 
duct remains  in  solution.  The  excess  of  tin  or  lead  salt  is  removed  by 
sulphuretted  hydrogen,  and  the  excess  of  baryta  by  sulphuric  acid.  With 
perchloride  of  tin,  after  the  removal  of  the  sulphuret  of  tin  and  expulsion 
of  the  sulphuretted  hydrogen,  the  hydrochloric  acid  is  to  be  separated  by 
suitable  means. 
In  individual  cases,  hy  the  ap^^^^cation  of  caustic  soda  or  potash  in  the 
place  of  the  hydrate  of  baryta,  perfect  solutions  are  obtained,  from  which 
the  potash  or  soda  compound  of  one  decomposition  product  is  separated 
in  an  insoluble  form  after  the  substance  under  examination  has  split  up. 
In  such  cases  it  is  naturally  advantageous  to  employ  soda  or  potash  instead 
of  baryta.  Generally,  the  potash  or  soda  compounds  separated  are  in- 
soluble only  in  potash  or  soda  solutions,  but  not  in  pure  water.  Conse- 
quently the  washing  must  be  performed  with  these  solutions.  The  filtered 
solution  is  carefully  saturated  with  sulphuric  acid,  evaporated,  and  the 
second  decomposition  product  removed  by  alcohol  from  the  alkaline  sul- 
phates, which  are  insoluble  in  that  menstruum. 
From  the  results  which  are  obtained  by  the  described  investigation  it 
it  may  be  determined  whether  by  the  treatment  vrith  acids  or  baryta  the 
substance  remains  unchanged  or  not,  or  whether  it  is  split  up  into  two  or 
more  products.  But  the  case  is  possible  that  after  the  treatment  with  acids  or 
alkalies,  no  two  decomposition  products  can  be  discovered,  although  the 
original  substance  no  longer  exists.  In  this  case,  where  only  one  substance 
results  in  the  place  of  another  by  the  action  of  acids  or  alkalies,  the 
original  substance  is  converted  into  a  new  body,  manifestly  under  the  re- 
ception of  the  elements  of  water,  or  the  expulsion  of  oxygen  and  hydrogen 
in  equal  equivalents  that  is  under  the  separation  of  water.  The  substance 
under  exmination,  therefore,  does  not  belong  to  the  class  of  copulated 
compounds. 
