rochleder's  proximate  analysis. 
465 
(Continued  from  page  376.) 
lead,  because  in  a  free  state  it  is  insoluble  in  water.  We  return  now  to 
the  fourteen  fluids. 
It  is  self-evident  that  we  have  not  to  deal  with  the  solutions  of  fourteen 
peculiar  bodies.  Several  bodies  may  be  contained  only  in  one,  or  at  the 
most  two  of  these  solutions,  but  another  constituent  may  exist  in  six  or 
eight  of  the  fluids,  and  each  contaminated  with  one  or  more  constituents, 
and  perhaps  in  one  of  these  fluids  quite  pure.  It  is  only  by  a  number  of 
reagents  that  the  truth  can  be  learnt.  It  is  clear  that  the  same  reagent 
must  be  always  applied  to  all  portions  of  the  fluids.  For  example,  we 
add  a  few  drops  of  a  solution  of  perchloride  of  iron  to  a  little  of  each  of 
the  fourteen  fluids  which  have  been  taken  for  this  purpose.  In  several  of 
the  portions  there  results  an  intense,  in  some  portions  a  less  intense,  in 
other  portions  no  coloration,  or  there  results  in  some  of  these  fourteen 
fluids  a  different  coloration  by  this  reagent  to  that  of  the  remainder.  In 
the  same  manner  we  add  a  second  reagent  to  portions  of  these  fourteen 
fluids,  and  so  forth.  By  these  means  it  may  be  ascertained  how  many  dif- 
ferent constituents  are  contained  in  the  fourteen  fluids.  It  may  further  be 
discovered  by  what  means  each  of  the  constituents  present  can  be  separa- 
ted from  the  remainder.  The  examination  can  only  be  conducted  further 
by  the  aid  of  elementary  analysis.  By  elementary  analysis  alone  can  the 
identity  of  a  discovered  body,  separated  from  its  accompanying  constitu- 
ents, be  proved  and  established  with  a  known  body.  The  similarity  of 
many  reactions  is  so  great  with  many  bodies,  that  we  should  regard  those 
as  identical  which  elementary  analysis  shows  us  are  very  different  bodies  : 
for  example,  two  members  of  a  series  of  homologous  substances  which 
stand  next  to  one  another  in  the  series,  See.  On  the  contrary,  bodies  often 
appear  different  in  many  of  their  properties  from  a  known  body,  while  we 
by  elementary  analysis  are  taught  that  a  complete  identity  exists,  and  the 
difference  in  many  properties  is  due  to  impurities  which  are  present  in  such 
small  quantities,  that  they  have  exercised  no  noticeable  influence  on  the 
result  of  the  analysis. 
§  6.  —  Quantitative  estimation  of  the  constituents. 
For  the  completion  of  a  work  on  the  analysis  of  vegetable  substances,  it 
is  appropriate  to  describe  the  methods  which  are  employed  to  determine 
the  quantities  of  individual  constituents  which  have  been  found  in  a  plant 
or  in  a  part  of  a  plant.  It  is  often  of  importance  in  pharmaceutical  or 
technical  relations  to  know  correctly  the  quantity  of  one  or  more  constitu- 
ents of  a  vegetable  substance,  or  more  rarely  those  of  a  whole  plant.  Instruc- 
tion for  the  complete  quantitative  analysis  of  a  vegetable  substance  cannot 
be  given  at  the  present  time,  as  scarcely  a  complete  qualitative  analysis  of 
any  one  plant,  or  part  of  a  plant,  exists.  It  is  self-evident  that  it  is  im- 
possible to  describe  methods  for  the  separation  of  bodies  which  are  un- 
known, whose  proportions  of  solubility  are  quite  as  unknown  as  their  com- 
30 
