Amsep^*xf7h7arm*}     Micro-Chemistry  of  Tea  Leaves.  457 
rated  nearly  to  dryness  on  the  water-bath  ;  the  extract  is  next  trans- 
ferred to  the  surface  of  a  thin  circular  disc  of  microscopic  covering- 
glass,  on  this  again  is  placed  a  thickish  ring  of  glass,  which  is  covered 
with  a  second  circular  disc  of  thin  glass,  the  whole  forming  what  I  will 
call  "  the  subliming  cell " — the  subliming  cell  is  placed  on  the  surface 
of  an  iron  plate,  which  carries  a  cup  of  mercury  in  which  is  inserted  a 
thermometer,  and  the  plate  is  fitted  in  the  ordinary  way  to  a  retort 
stand.  This  method  of  sublimation,  in  all  its  essential  features,  is 
identical  with  the  one  proposed  and  employed  years  ago  by  Dr.  Guy. 
On  heating  the  iron  plate,  first,  moisture  is  given  off  and  condenses  on 
the  cover  of  the  subliming  cell,  and  this  cover  may  be  removed  and 
replaced  by  a  second.  In  a  very  short  time  after  it  has  become  dry,  a 
light  mist  is  seen  on  the  upper  disc,  and  this  mist  the  microscope 
resolves  into  beautifully  distinct  little  crystals  of  thein  ;  they  may  be 
identified  as  thein  by  re-subliming,  when  it  will  be  found  they  will  rise 
to  the  upper  disc  at  about  the  temperature  of  10 1°  C.  The  sublim- 
ing temperature  of  the  extract  itself  is  rather  variable ;  the  extract 
should  be  heated,  if  no  mist  or  crystals  become  visible,  up  to  as  high 
as  220°  C,  and  if  still  no  crystals  are  obtained,  the  substance  most 
certainly  contains  no  thein.  In  all  my  experiments  I  have  always 
obtained  a  sublimate  from  genuine  products  derived  from  tea  or  coffee 
below  2000  C. 
(2.)  The  substance  is  boiled  and  treated  with  magnesia  as  before,, 
the  solution  cooled,  a  bit  of  dialysing  parchment  folded  and  cut  into  a 
miniature  filter  form,  and  placed  in  a  glass  tube,  which,  as  very  small 
quantities  are  being  dealt  with,  need  be  no  bigger  than  a  thimble,  or  a 
porcelain  crucible  may  be  used,  which  beihg  always  at  hand  will,  per- 
haps, be  more  convenient  than  anything  else.  The  solution  is  then,, 
by  this  little  dialysing  apparatus,  which  I  need  not  further  detail,  dia- 
lyzed  for  twelve  hours  ;  a  yellow  coloring  matter  and  thein  are  found 
in  the  outer  liquid  ;  a  microscopic  examination  of  this  liquid,  when 
evaporated  down  will  readily  discover  crystals  of  thein.  As  in  the 
former  case,  the  fragments  of  the  leaf  or  the  leaf  itself  is  uninjured, 
and  can  be  put  to  any  supplementary  examination  desired. 
(3.)  The  leaf  is  boiled  for  a  minute  or  two  in  a  watch  glass,  with  a 
very  little  water,  a  portion  of  magnesia  equal  in  bulk  is  added,  and  the 
whole  heated  to  boiling,  and  thus  rapidly  evaporated  down  to  a  good- 
sized  drop  ;  this  drop,  containing  yellow  coloring  matter,  magnesia  and 
