rochleder's  proximate  analysis. 
85 
quantity  of  the  liquid  when  a  little  shall  be  dissolved  therein.  How- 
ever, when  it  is  desired  to  exhaust  as  much  as  possible  a  substance  by 
means  of  a  liquid,  it  is  necessary  to  empl  )y  a  large  quantity  of  the 
liquid,  as  it  is  essential  to  effect  the  extraction  with  renewed  portions 
of  the  solvent.  In  so  great  a  quantity  of  liquid,  a  quantity  not  inconsidera- 
ble of  the  very  difficultly  soluble  bodies  dissolve,  which,  by  the  concentra- 
tion of  the  liquid,  are  often  prevented  from  being  separated  by  other  con- 
stituents, thus  rendering  impure,  in  a  serious  degree,  the  substance  which 
we  wish  to  extract  free  from  the  other  constituents. 
The  method  for  the  analysis  of  plants,  given  in  the  following  pages,  de- 
pends on  the  treatment  of  materials  with  various  solvents.  Every  result- 
ing solution  then  undergoes  a  further  appropriate  treatment  therein.  It 
must  be  here  mentioned  that  the  preparation  of  some  of  these  solutions,  and 
their  further  invesdgation,  promise  no  certainty,  and  that  only  by  a  com- 
parison of  the  results  which  are  obtained  by  the  investigation  of  all  the  in- 
dividual constituents,  separately  and  collectively,  can  we  deduce  a  correct 
conclusion  on  the  constitution  of  a  vegetable  product. 
It  would  have  been,  as  every  competent  judge  will  concede,  a  perfectly 
unfruitful,  useless  labor,  to  publish,  as  far  as  it  is  known,  the  behaviour  of  all 
known  constituents  of  plants  with  reagents  ;  and  more  so,  because  we  would 
but  deceive  ourselves  or  others  if  from  the  apparently  identical  behaviour 
of  two  analogous  bodies  with  some  reagents  a  conclusion  with  regard  to  their 
identity  should  be  drawn.  Only  by  identical  composition,  surely  established 
by  elementary  analysis,  the  identity  of  reactions  proves  something;  through 
the  attempts  at  recognizing  and  detecting  in  a  mixtuie  of  bodies  the  indi- 
vidual constituents  by  their  behaviour  with  reagents  without  further  corrob- 
oration, have  arisen  numberless  false  statements.  Malic  acid,  gum,  &c., 
are  stated  to  have  been  found  as  constituents  in  numerous  plants.  Who- 
ever has  carefully  tested  these  statements  will  find,  by  a  repetition  of  the 
analysis,  no  mulic  acid,  and  convince  himself  that  the  supposed  gum  is  a 
salt  of  an  organic  acid  with  an  inorganic  base,  which  possesses  no  remark- 
able taste,  dries  to  a  gum-like  mass,  dissolves  in  water,  and  is  precipitated 
by  alcohol  therefrom  in  white  flocks,  &c.  To  prove  that  a  body,  which  has 
been  obtained  by  analysis,  is  identical  with  an  already  known  substance, 
the  elementary  analysis  of  this  body,  or  one  of  its  suitable  combinations, 
must  be  undertaken.  Only  the  reactions  of  substances  rendered  pure,  de- 
serve in  this  respect  consideration,  not  the  reactions  of  mixtures.  With- 
out elementary  analysis,  in  regard  to  identity,  only  a  high  degree  of  pro- 
bability can  be  arrived  at,  but  no  certainty.  But  an  error,  in  a  high  de- 
gree prO)bable,  is  more  dangerous  than  a  palpable  mistake.  Elementary 
analyses,  which  alone  bestow  a  value  on  the  identity  of  reactions,  are, 
besides,  the  least  difficult  and  tedious  part  of  the  labor.  They  require  no 
great  amount  of  ability.  This  is  only  necessary  for  the  preparation  of  the 
substance  to  be  anal^^zed. 
