Detection  of  the  Adulteration  of  Tea.  549 
to  contain  catechu,  starch,  magnesia,  metallic  iron,  graphite,  sand, 
&c.  He  had  also  found  sloe  leaves  presenting  a  close  resemblance 
to  green  tea  in  every  respect.  An  inspection  of  the  specimens  an- 
alyzed showed  that  genuine  green  teas  were  richer  in  tannin  than 
black  teas  in  about  the  proportion  of  two  to  three.  This  was  no  doubt 
due  to  the  partial  oxidation  and  destruction  of  the  tannin  during  the 
process  of  fermentation  to  which  black  tea  is  subjected  in  the  process 
of  manufacture.  Whether  the  acknowledged  superior  strength  of 
green  tea  was  due  to  the  larger  percentage  of  tannin  present  in  it,  he 
was  not  prepared  to  say.  The  determination  of  theina  he  had  made 
did  not  account  for  the  difference,  and  most  analysts  had  found  more 
theina  in  black  than  in  green  tea.  The  infusion  of  green  tea  was  not 
nearly  so  strong  in  color  as  that  of  black  tea,  though  it  was  half  as 
strong  again  in  tannin,  so  that  the  depth  of  color  could  not  be  regard- 
ed as  a  proof  of  strength,  though  generally  so  considered.  If  a  solu- 
tion of  carbonate  of  sodium  be  added  to  a  weak  infusion  of  tea  (strained 
away  from  the  leaves)  a  considerable  darkening  was  observed,  though 
certainly  the  infusion  could  become  no  stronger.  Thoroughly  ex- 
tracted tea  leaves  yield  a  brown  liquid  when  treated  with  carbonate 
of  sodium  solution.  These  facts  quite  explained  why  careful  house- 
wives had  a  fancy  for  putting  soda  in  the  teapot,  the  infusion  becom- 
ing sensibly  darker  by  the  addition,  to  say  nothing  of  the  extra  color- 
ing matter  from  the  leaves.  Apart  from  its  softening  effect  on  the 
water  (the  advantage  of  which  he  thought  was  doubtful),  there  could 
be  no  good  reason  for  its  addition.  In  the  methods  he  had  used  for 
detecting  facing  and  coloring  there  was  not  much  that  was  new.  On 
treating  the  tea  with  warm  water  the  colors  and  facings  came  off,  and 
on  straining  off  the  leaves  and  leaving  the  liquid  at  rest,  they  grad- 
ually settled  to  the  bottom.  If  prussian  blue  or  indigo  were  present 
the  sediment  generally  had  a  bluish  or  greenish  color,  and  the  tests 
for  these  pigments  must  be  tried  accordingly.  Magnesia  was  often 
present  both  in  the  free  state  and  as  insoluble  silicate.  This  latter 
facing  he  had  found  on  several  occasions  on  green  teas  of  peculiarly 
smooth  appearance  and  slippery  feel.  It  was  detected  by  heating 
the  sediment  with  hot  hydrochloric  acid,  and  then  with  solution  of 
caustic  soda.  The  residue  was  ignited  and  fused  with  alkaline  car- 
bonate, the  first  product  dissolved  in  acid,  evaporated  to  dryness,  re- 
dissolved  in  weak  acid,  the  solution  treated  with  ammonia  and  oxa- 
late of  ammonium,  the  precipitate  filtered  off,  and  the  clear  liquid  tested 
