560 
Analysis  of  Tea. 
f  Am.  Jour.  Pha rnfl 
1      Dec,  1876 
and  49*800  grams  potassium  iodide  in  water  to  make  one  litre.  To 
the  clear  and  dilute  decoction  of  one  gram  of  the  tea,  obtained  as 
above  described,  the  cinchonia  solution  is  added  from  the  burette  to 
slight  excess  and  the  quantity  noted,  the  mixture  filtered  and  the  residue 
washed.  Unless  some  means  for  "rapid  filtration  "  be  used,  this  part 
of  the  operation  is  very  slow,  but  with  any  "  filter  pump  "  it  is 
altogether  satisfactory.  To  the  filtrate  with  the  washings  the  iodide 
solution  is  added,  stirring  until  the  precipitate  is  complete.  The  pre- 
cipitate subsides  quickly,  and  a  drop  of  the  clear  solution  on  a  blue  or 
black  glass  slide  treated  with  a  drop  of  the  reagent  (from  the  burette) 
will  show  if  farther  precipitate  can  be  obtained  (the  drops  so  taken 
being  then  rinsed  into  the  mixture  tested).  Each  cc.  of  the  iodide 
solution  precipitates  0*0102  gram  of  cinchonia,  or  0*0124  gram  of 
cinchonia  sulphate,  or  2*74  cc.  of  Wagner's  standard  solution  of  cin- 
chonia sulphate.  Each  cc.  of  the  last  named  solution  precipitates  o*oi 
gram  of  tannic  acid.  Having  the  decoction  of  one  gram  of  tea  :  cc. 
cinchonia  sol. — (2.74XCC  iodide  sol.)=per  cent,  of  tannin .  (in  its 
equivalent  of  tannic  acid). 
The  reports  of  the  proportion  of  tannin  in  tea  show  remarkable 
differences.  A.  H.  Allen,  by  volumetric  determination  with  lead 
acetate  as  previously  described,  finds  about  20  per  cent,  tannin  in  green 
tea  and  an  average  of  10  per  cent,  in  black  tea.  G.  W.  Wigner 
("Phar.  Jour.  Trans."  [3],  vi.,  281),  by  same  method,  found  in 
Assam  33  per  cent,  and  45*5  per  cent.;  in  Young  Hyson  39  per  cent, 
and  another  39  per  cent.;  in  mixed  Caper  42*3  percent.  The  Young 
Hyson  giving  45*5  per  cent,  was  a  mixture  of  six  samples.  Dragen- 
dorfF  ("  Werthbestimmung,"  1874,  p.  60)  quotes  green  tea  at  12*32 
and  12*70  per  cent,  of  tannic  and  boheic  acids,  and  a  sample  of  black 
tea  9*42  per  cent.  Mr.  Allen  and  Mr.  Wanklyn  take  the  average  of 
tannin  in  black  tea  at  10  percent,  for  a  basis  of  calculation  of  presence 
and  proportion  of  spent  tea. 
The  total  ash  was  obtained  by  the  incineration  of  one  gram  of  tea 
in  a  weighed  crucible.  For  the  soluble  ash,  the  total  ash  was  washed 
on  a  filter  with  hot  water  till  the  washings  gave  no  residue,  the  residual 
ash  dried  and  weighed,  and  the  difference  of  weight  taken. 
The  samples  were  obtained  from  the  retail  trade  in  Michigan. 
