Having  progressed  thus  far  in  the  examination  of  the  article,  we  are
in  a  position  to  scrutinise  samples  of  it,  with  a  view  to  the  detection  of
adulteration.  Knowing  well  the  structures  which  are  met  with  in  the
genuine  article,  we  shall  experience  but  little  difficulty  in  determining
whether  the  sample  contains  any  foreign  or  extraneous  vegetable  sub-
stance, or  consists  entirely  of  the  one  article.
Having  determined  that  it  does  contain  such  foreign  substance,
the  next  thing  is  to  endeavour  to  ascertain  the  nature  of  this,  and  to
refer  it  to  the  plant  or  substance  to  which  it  belongs.  The  facility
with  which  this  is  done  depends  upon  the  extent  of  our  acquaintance
with  other  vegetable  substances.  If  this  be  considerable,  a  glance  is
often  sufficient  to  determine  this  point.
However,  it  is  not  requisite  in  all  cases  that  we  should  possess
A  knowledge  of  the  structure  and  appearances  presented  by  any  very


BY   CHEMISTRY.  55

great  number  of  vegetable  productions,  since  a  few  articles  are  con-
stantly employed  for  adulteration  in  the  case  of  very  many  and  widely
different  articles,  such  as  wheat  flour,  potato  starch,  sago  powder,  rice,
&c. ;  and  all  that  is  necessary  in  such  cases  is  that  we  should  be  able  to
recognise  these  substances  when  we  meet  with  them.
Most  vegetable  substances  are  made  up  of  certain  structures  and
elements,  as  cellular  tissue,  woody  fibre,  vessels,  starch  granules,  &c.
