rochleder's  proximate  analysis. 
177 
[Continued  from  page  88.] 
plant  which  produces  it.  We  know  infinitely  more  of  the  cinchona-tree 
and  other  exotic  plants  than  of  the  lime  and  nut  trees  of  our  own  woods. 
If  all  chemists  were  to  occupy  themselves  with  the  analyses  of  plants,  after 
several  centuries  there  would  be  still  materials  enough  growing  before  their 
eyes  to  employ  hundreds  of  hands  with  their  chemical  investigation. 
The  investigations  which  spread  the  most  light  are  those  which  enable  us 
to  learn  the  composition  of  the  individual  parts  of  a  plant  at  different 
periods  of  its  growth,  and  at  different  epochs  of  its  development.  The  ma- 
terial for  such  investigations  can  scarcely  be  procured  at  a  distance,  so  we 
are  constrained  to  examine  that  which  lies  near  us,  and  not  to  seek  afar  off 
that  which  is  better  and  easier  obtained  at  home. 
With  regard  to  the  quantity  of  material  required  for  the  investigation,  no 
certain  weight  or  measure  as  a  minimum  can  be  fixed.  But  it  is  better  in 
all  cases  to  employ  too  much,  rather  than  too  little,  material.  With  ma- 
terials which  cannot  be  procured  in  any  required  or  unlimited  quantity,  it 
is  better  to  commence  no  analysis.  Through  a  scarcity  of  material  the 
operator  is  constrained  to  terminate  the  research,  unable  to  complete  it, 
and  has  time  and  money  uselessly  spent,  or  he  arrives  at  incorrect  results, 
when,  from  a  failure  of  the  material,  he  is  unable  to  undertake  a  number 
of  control  experiments.  It  is  on  that  account  that  the  results  of  analyses 
which,  as  frequently  happens,  were  undertaken  with  a  few  ounces  of  the 
material,  seldom  possess  any  value.  In  the  best  instances  of  such  analy- 
ses some  constituents  were  overlooked  which  were  present  in  small  quan- 
tities in  the  material.  Many  incorrect  statements  are  made  in  such 
analyses  because  an  insufficient  number  of  methods  of  separation  were  em- 
ployed. Mixtures  of  bodies  are  regarded  as  new  substances,  and  are 
long  carried  on  as  the  ballast  of  science,  until  later  analyses  prove  their 
non-existence.  Substances  which  are  widely  different  from  one  another 
are  confounded  with  each  other,  because  an  insufficiency  of  material  wag 
employed  to  prepare  enough  of  the  constituent  to  establish  its  composition 
in  the  pure  state.  Thus,  one  chemist  finds  tartaric  acid,  when  another  is 
stated  to  have  found  oxalic  acid,  and  a  third  seeks  unsuccessfully  for  tar- 
taric acid,  and  finds  instead  citric  acid.  If  we  could  previously  determine 
the  quantity  of  material,  it  would  often  be  useful,  but  such  a  previous  deter- 
mination is  impossible.  The  operator  can  easily  ascertain  how  much  water 
or  dry  substance  a  material  contains  ;  and  when  it  is  very  rich  in  water,  con- 
cludes therefrom  that  he  will  require  proportionately  more  of  it  than  from 
one  poor  in  water  under  other  similar  conditions.  But  from  the  abundance 
of  dry  substance,  no  conclusion  can  be  drawn  as  to  the  quantity  which  will 
be  required  for  the  investigation.  Many  parts  of  plants  contain  large 
quantities  of  cellulose,  starch,  and  other  ordinary  constituents,  which 
may  be  readily  detected,  but  little  of  the  remaining  constituents. 
Frequently  all  the  constituents  are  present  in  rather  considerable  quan- 
tities, so  that  the  investigation  can  be  terminated  with  a  little  material, 
unless  one  constituent  is  present  in  very  small  quantity.  In  such  a  case  a 
12 
