468 
rochleder's  proximate  analysis. 
of  a  constituent  is  by  no  means  new.  For  a  long  time  we  have  known 
how  to  estimate  the  contents  of  sugar  from  the  quantity  of  alcohol  which 
is  obtained  by  the  fermentation  of  the  sugar.  We  have  had  processes  for 
the  estimation  of  starch  from  the  quantity  of  sugar  which  can  be  produced 
from  starch  by  various  agents.  Indirect  estimations  of  this  kind  are  often 
very  easily  performed  in  cases  where  a  direct  determination  is  endlessly 
difficult,  or  quite  impossible.  To  estimate  the  quantity  of  caincic  acid  in 
the  roots  of  Chiococca  racemosa  belongs  to  the  impossible  ;  the  caffeo-tan- 
nic  acid  cannot  be  so  exactly  separated  from  the  caincic  acid,  that  the 
latter  is  obtained  pure  without  loss.  The  caffeo-tannic  acid  mixed  in 
its  watery  solution  with  hydrochloric  acid  and  heated,  does  not  give 
an  insoluble  or  difficultly  soluble  decomposition  product,  but  simply 
caincic  acid.  When  a  mixture  of  both  substances  is  treated  in  the  heat 
with  dilute  hydrochloric  acid,  the  decomposition  product  of  caincic  acid  is 
easily  obtained,  and  its  quantity  can  be  estimated.  This  product  is  very 
difficultly  soluble,  but  not  insoluble,  in  the  fluid  from  which  it  has  sepa- 
rated. We  know,  by  the  examination  which  has  been  made,  how  much 
per  cent,  of  the  difficultly-soluble  decomposition  product  is  afforded  by  the 
pure  caincic  acid,  and  we  know  the  solubility  of  this  decomposition  pro- 
duct as  well  as  the  quantity  of  fluid,  consequently  know  the  quantity  of 
the  decomposition  product  which  remains  dissolved  therein ;  and  thus  we 
can  estimate,  in  a  short  time,  the  quantity  of  caincic  acid  with  the  greatest 
facility  and  exactness.  Indirect  determinations  of  that  kind  may  be  per- 
formed, in  a  number  of  cases,  without  any  difficulty  and  in  a  very  short 
time.  The  correction  first  employed  by  Fresenius  in  mineral  analysis  for 
the  solubility  of  difficultly  soluble  precipitates  must  not  be  passed  over  here 
without  attention  being  drawn  to  it. 
MICROSCOPIC  EXAMINATION  WITH  THE  AID  OF  REAGENTS. 
Repeatedly  the  assertion  has  been  made,  that  a  chemical  analysis  can 
only  be  considered  as  completed  when  it  not  only  enables  us  to  learn  the  con- 
stituents of  a  vegetable  substance,  but,  with  the  assistance  of  the  micro- 
scope, renders  us  so  experienced  that  we  know  in  which  form,  and  at  what 
place,  to  find  the  individual  constituents  in  the  material  under  examina- 
tion, and  make  out  whether  they  are  in  the  form  of  crystals  or  in  the  form 
of  amorphous  masses,  or  exist  in  a  dissolved  form  in  the  contents  of  the 
cells,  or  as  a  constituent  of  the  walls  of  the  cell ;  also  the  density  of  its 
layers,  and  so  forth.  It  is  certain  that  we  can  only  then  say  we  know  a 
plant  or  its  parts  when  our  investigations  in  chemical  and  anatomical  di- 
rections are  equally  complete,  and  at  the  same  time  consolidated  to  a  whole. 
But  the  assertion  quoted  is  decidedly  untrue  from  a  chemical  point  of 
view,  if  correct  from  a  botanical  or  a  vegeto-physiological  one.  The  chem- 
ical investigation  has  only  to  teach  us  the  problem  what  constituents  a 
plant  contains,  and  in  what  quantities  which  naturally  fluctuate  between 
two  certain  extremes. 
