48 
Examination  of  Chinese  Tea. 
f Am.  Jour.  Pharm. 
i.       Jan.,  lt>92. 
EXAMINATION  OF  CHINESE  TEA.1 
By  P.  Dvorkovitch. 
The  author  criticizes  the  methods  of  Peligot,  Mulder,  and  Zoller 
for  the  estimation  of  theine  in  tea,  and,  regarding  them  as  unsatis- 
factory, has  devised  the  following  process,  which  is  said  to  be  both 
rapid  and  exact.  Ten  grams  of  the  finely  powdered  tea  is  treated 
with  three  successive  quantities  of  200  cc.  of  boiling  water,  five 
minutes  being  allowed  for  each  digestion,  and  then  boiled  with  two 
successive  quantities  of  200  cc.  of  water,  or  more,  if  necessary,  until 
the  last  extract  is  almost,  if  not  quite,  free  from  color.  The  extracts 
are  made  up  to  a  litre,  and  extracted  thrice  with  light  petroleum  to 
remove  oil,  etc.;  600  cc.  of  the  washed  solution  is  then  shaken  with 
IOO  cc.  of  baryta-water  containing  4  grams  of  baryta  in  solution, 
filtered,  and  583  cc.  of  the  filtrate  (corresponding  with  5  grams  of 
tea)  mixed  with  100  cc.  of  salt  solution  (20  grams  of  salt  in  100  cc. 
of  water),  and  thrice  extracted  with  chloroform.  The  extraction  is 
best  effected  by  shaking  successive  small  quantities  of  the  solution 
with  chloroform,  since  nothing  further  can  be  extracted  from  the 
solution  after  the  third  shaking  under  these  conditions,  and  not 
more  than  400  grams  of  chloroform  is  required.  After  removal  of 
the  chloroform,  by  distillation  to  a  small  bulk  and  subsequent 
evaporation  in  a  small  dish  and  drying  at  100°,  the  theine  is  obtained 
in  perfectly  white  needles. 
In  the  preparation  of  black  tea  the  leaves  are  submitted  to  a 
fermentation,  which  has  a  most  important  influence  on  the  quality 
of  the  product,  and,  as  Geissler  has  shown,  is  carried  on  at  the 
expense  of  the  tannin.  With  the  object  of  estimating  not  only  the 
tannin  but  also  the  decomposition  products  formed  from  it  during 
the  fermentation,  or,  in  other  words,  determining  the  extent  of  the 
fermentation,  the  author  has  improved  Lbwenthal's  method  ot 
oxidation  with  potassium  permanganate  in  the  presence  of  indigo- 
carmine.  The  solutions  required  are  the  following  :  (1)  Decinor- 
mal  oxalic  acid;  (2)  a  potassium  permanganate  solution  of  such  a 
strength  (approximately  2-6  grams  in  the  litre)  that  130  grams  are 
equivalent  to  100  grams  of  decinormal  oxalic  acid;  (3)  dilute  sul- 
phuric acid  containing  200  grams  of  ordinary  acid  to  a  litre  of 
water;  (4)  baryta-water  containing  4  grams  of  baryta  to  100  cc.  of 
1  Berichte,  24,  1945-1955  ;  reprinted  from  Jour.  Chem.  Soc,  1891,  p.  1302. 
