82 
rochleder's  proximate  analysis. 
The  second  part  of  the  fluid  is  mixed  with  acetic  acid,  to  ascertain 
whether  a  precipitate  results.  If  a  precipitate  ensues, it  is  collected  on  a 
filter,  of  which  several  small  ones  are  used,  instead  of  a  large  one.  The 
filtered  fluid  is  now  heated,  whereby  generally  a  coagulum  is  formed.  The 
substance  precipitated  by  a  little  acetic  acid  is  examined,  to  learn  whether 
it  is  quite  or  partially  soluble  or  not  in  acetic  acid  when  an  excess  is 
added.  By  these  means  a  separation  of  several  of  these  bodies  may  be 
sometimes  effected. 
The  ihirdpart  is,  lastly,  mixed  with  alcohol,  and  it  is  observed  whether  a 
precipitate  results,  which  nearly  in  all  cases  makes  its  appearance  thereby 
in  at  least  a  small  quantity.  The  precipitate  collected  on  a  filter  and  washed 
with  spirit,  is  treated  with  water,  whereby  only  in  few  cases  a  complete 
solution  results.  The  filtered  aqueous  solution  resulting  is  heated,  by 
which  frequently  a  considerable  coagulum  is  thrown  out. 
III. — Examination  of  the  extract  obtained  by  acidulated  water. 
As  already  stated  (page  181),  thisextract  is  employed  for  the  detection 
of  some  organic  acids,  which  per  se  are  soluble  in  water,  but  are  contained 
in  the  material  under  examination  in  the  form  of  compounds,  mostly  as 
lime  salts,  which  are  neither  soluble  in  pure  water  nor  in  spirit.  It  is  also 
employed  for  the  detection  of  organic  bases.  For  example,  when  a  part 
of  a  plant  contains,  as  is  frequently  the  case,  oxalate  of  lime,  the  oxalic 
acid  is  neither  found  in  the  watery  decoction  nor  in  the  spirituous  extract, 
because  oxalate  of  lime  is  equally  insoluble  in  water  and  in  spirit.  By  its 
decomposition,  by  means  of  sulphuric  acid,  which  is  added  to  the  water,  we 
obtained  from  the  salt  insoluble  in  water  so  much  oxalic  acid  in  a  free 
state,  that  we  can  detect  it  in  the  fluid. 
For  its  further  investigation  the  acid  extract  is  freed  from  its  sulphuric 
acid  by  carbonate  of  baryta,  which  is  added  in  small  quantity.  A  precipi- 
tate of  sulphate  of  baryta  thereby  ensues,  mixed  with  more  or  less  com- 
pounds of  organic  substances,  or  perhaps  with  precipitated  organic  bases, 
when  they  were  present  in  the  ncid  solution,  and  one  or  more  of  them  were 
difficultly  soluble  or  insoluble  in  water.  The  precipitate  is  collected  on  a 
filter  and  washed  with  water.  The  washed  precipitate  is  boiled  with  strong 
spirit,  and  the  spirituous  solution  is  separated  from  the  insoluble  matter 
by  a  filter.  It  is  ascertained  whether  the  spirit  has  dissolved  or  not  any 
organic  bases.  The  baryta  precipitate,  boiled  with  spirit,  is  digested  with 
dilute  sulphuric  acid,  to  produce  sulphate  of  baryta,  which  is  separated  by 
a  filter,  and  to  obtain  a  solution  of  the  substance  which  was  combined  with 
the  baryta.  The  lime  and  baryta  salts  generally  exhibit  a  very  analogous 
degree  of  solubility,  so  that  by  this  method  mostly  those  compounds  are 
obtained  in  solution  whose  lime  salts  being  insoluble  in  water  and  spirit, 
could  not  be  extracted  by  these  fluids  from  the  material  under  examina- 
tion.   The  fluid  which  is  filtered  from  the  sulphate  of  baryta,  excess  of 
