rochleder's  proximate  analysis. 
471 
in  an  approximately  pure  condition,  the  next  problem  is  to  completely  pu- 
rify these  bodies.  This  completely  pure  preparation  of  bodies  is  attended 
often  with  no  difficulty,  as,  for  example,  is  the  case  with  easily  crystalliza- 
ble  bodies  or  with  volatile  bodies  when  they  exist  with  non-volatile  bodies, 
or  even  with  volatile  ones  if  in  reference  to  their  chemical  characteristics 
they  are  widely  different.  Generally,  bodies  of  the  opposite  character  of 
an  acid  and  a  base  are  easily  obtained  pure  when  they  are  at  the  same 
time  present  with  indifferent  substances  ;  likewise  all  bodies  which  are 
not  per  se  crystallizable  when  they  are  capable  of  forming  compounds, 
which  can  be  readily  obtained  in  a  crystalline  state.  On  the  contrary,  it 
is  extremely  difficult  to  completely  separate  indifferent  amorphous  sub- 
stances when  they  exist  mixed  with  one  another,  and  to  prepare  in  a  state 
of  purity  the  individual  constituents  of  such  mixtures.  But  the  pure  pre- 
paration is  often  not  the  greatest  difficulty,  but  the  establishment  of  the 
proof  that  the  substance  has  been  prepared  in  a  state  of  purity.  It  is  of- 
ten possible  to  effect  the  pure  preparation  of  a  substance,  but  we  have  no 
index  of  the  purity  of  the  prepared  substance.  This  is  often  the  case  with 
the  amorphous  and  indifferent  constituents  of  vegetables.  There  is  fre- 
quently no  other  means  for  obtaining  certainty  with  regard  to  the  purity 
of  a  substance  than  by  elementary  analysis,  conducted  with  portions  of 
the  substances  which  have  been  prepared  in  different  ways  from  the  same 
part  of  the  plant,  or  where  possibly  taken  from  different  parts  of  the  plant. 
The  complete  agreement  in  the  results  of  the  analysis  of  the  different  por- 
tions of  the  same  substance  affords  a  proof  of  its  purity.  The  individual 
constituents  which  we  have  prepared  in  a  pure  isolated  condition  are  sub- 
mitted to  a  further  chemical  examination.  The  elementary  analysis  of 
these  substances  combined  with  their  reactions,  will  supply  us  with  an  ev- 
idence whether  the  constituent  found  is  or  is  not  identical  with  a  body  al- 
ready known.  A  close  examination,  to  the  execution  of  which  the  pre- 
vious analysis  will  afford  assistance,  will  now  teach  us  the  constitution  of 
the  individual  constituents.  From  this  knowledge  an  insight  is  obtained 
into  the  connection  between  the  individual  constituents,  that  is  to  say,  our 
investigation  will  afford  results  quite  as  useful  for  vegetable  physiology  as 
for  chemistry  itself.  We  secure  an  important  advantage  by  these  investi. 
gations,  when  we  make  the  objects  of  our  studies  not  only  the  various  in- 
dividual parts  of  a  plant,  but  also  the  various  individual  parts  in  different 
epochs  of  their  development.  Observations  on  the  formation  of  a  body 
from  one  or  several  others  will  bring,  most  easily,  light  into  the  darkness 
in  which  the  transformation  of  vegetable  bodies  is  wrapped  up.  Correct 
analyses  of  plants,  or  rather  of  their  parts,  in  their  various  relations,  and 
their  gradual  development  consequently,  are  a  means  to  enlarge  in  a  very 
productive  manner,  not  only  our  chemical,  but  also  our  physiological  know- 
ledge. In  the  hope  of  having,  by  the  present  work  on  the  analysis  of 
plants  and  their  parts,  contributed  something  towards  the  accomplishment 
