rochleder's  proximate  analysis. 
83 
carbonate  of  baryta  and  organic  baryta  compounds,  and  perhaps  pre- 
cipitated organic  bases,  is  then  mixed  with  sulphate  of  copper,  whereby 
sulphate  of  baryta  is  precipitated,  when  a  soluble  baryta  salt  has  been 
formed  and  is  contained  in  the  fluid,  as  well  as  many  compounds  of  the 
oxide  of  copper  with  organic  substances.  The  precipitate  is  filtered  off, 
washed  with  water,  and  decomposed  under  water  by  sulphuretted  hydrogen. 
The  undecomposed  sulphate  of  baryta  and  sulphuret  of  copper  are  filtered 
off,  and  a  watery  solution  of  the  organic  substances  which  were  combined 
with  the  oxide  of  copper  is  thus  obtained.  The  filtrate  is  heated,  for  the 
expulsion  of  the  sulphuretted  hydrogen,  in  a  flask  or  a  tubulated  retort,  in 
a  water  bath,  during  which  a  stream  of  carbonic  acid  is  led  through  the 
liquid.  After  this  the  fluid  is  mixed  with  subacetate  of  lead  as  long  as  a 
precipitate  ensues.  By  these  means  all  the  acids  not  precipitated  by  the 
copper  salt,  with  few  exceptions,  are  thrown  down.  The  precipitate,  after 
it  has  been  collected  on  a  filter  and  washed  with  water,  is  boiled  with 
alcohol,  to  extract  the  bases  possibly  precipitated  with  the  lead  compounds. 
With  these  some  lead  salts  may  of  course  be  dissolved  at  the  same  time. 
The  spirit  is  distilled  from  the  fluid,  which  has  previously  been  freed 
from  lead  by  sulphuretted  hydrogen,  and  the  bases  are  sought  in  the 
aqueous  fluid  filtered  from  the  sulphuret  of  lead.  The  fluid  filtered  from 
the  precipitate  produced  by  basic  acetate  of  lead,  contains  in  the  majority 
of  cases  the  organic  bases.  The  bases  thus  separated  from  most  other 
bodie|s  can  be  easily  discovered  therein.  A  portion  of  this  fluid  is  em- 
ployed for  the  detection  of  volatile  bases,  and  another  portion  for  the  dis- 
covery of  the  bases  not  distillable  with  water,  according  to  the  directions 
which  are  given  on  these  points  in  the  examination  of  the  watery  decoc- 
tion (pages  274,  369,  468.) 
The  acid  fluid  which  has  been  obtained  by  the  digestion  of  the  mixture  of 
baryta  salts  with  dilute  sulphuric  acid  is,  by  means  of  fractional  precipita- 
tion, employed  for  the  detection  of  the  acids  contained  therein.  Acetate  of 
baryta  is  used  for  the  fractional  precipitation,  which  gives  better  results 
in  this  case  than  acetate  of  lead. 
Volatile  as  well  as  non-volatile  bases  can  indeed  be  separated  in  a 
shorter  way  from  the  acid  extract :  the  former,  by  mixing  the  acid  ex- 
tract with  an  excess  of  a  solution  of  potash  and  distillation  :  the  latter, 
by  infusion  of  galls  and  the  like  precipitants.  But  thereby  we  run  in 
danger  of  overlooking  some  other  constituents.  On  this  account  the  cere- 
monious method  of  analysis  here  described  is  to  be  preferred. 
IV. — Examination  of  the  extract  obtained  by  ammoniacal  water. 
This  extract,  as  already  mentioned  (p.  181),  is  mixed  with  dilute  hy- 
drochloric acid,  and  the  resulting  precipitate,  if  any,  collected  on  a  filter, 
and  washed  with  water.  The  precipitate  is  treated  with  hot  spirit,  to 
learn  whether  a  portion,  or  the  whole,  of  the  precipitate  dissolves  or  not  in 
