Am.  Jour.  Pharn  . 
Aug.,  1880. 
Indigo  in  Bengal, 
415 
Mulhouse,"  gives  some  interesting  particulars  of  the  preparation  of 
indigo  in  Bengal. 
In  this  province  of  India,  the  indigo  factories — in  addition  to  filters, 
presses,  a  boiler,  drying  grounds  and  reservoirs— are  provided  with  two 
rows  of  vats,  each  consisting  of  15  to  20.  These  vats  are  constructed 
of  brick-work,  and  covered  over  wiih  a  strong  coating  of  stucco ; 
they  are  generally  from  18  to  20  feet  square,  and  about  3  feet  deep; 
the  back  row  is  nearly  three  feet  higher  than  the  front,  and  it  is  in  the 
higher  row  of  vats  that  the  fermentatation  takes  place.  When  the 
fermentation  is  completed,  the  liquid  is  turned  off,  and  flows  into  the 
lower  vats.  The  water  of  the  Ganges,  which  is  comparatively  pure, 
and  therefore  well  adapted  for  the  purpose,  is  utilized  in  this  process. 
In  the  morning  the  plant  is  cut,  taken  to  the  factory,  and  loaded  in 
the  vats  in  the  evening,  one  vat  containing  100  packages  or  bundles, 
arranged  in  layers,  on  the  top  of  which  are  placed  transverse  pieces  of 
wood  tightly  wedged  down,  it  being  necessary  that  the  plants  should 
be  well  pressed,  or  the  fermentation  would  not  otherwise  thoroughly 
take  place.  Water  is  then  allowed  to  flow  into  the  vats  until  the 
plants  are  submerged.  The  process  of  fermentation  lasts  from  nine  to 
fourteen  hours,  but  depends  entirely  upon  the  temperature.  To  test 
the  progress  of  the  operation,  a  little  of  the  liquid  is  drawn  off  into 
the  lower  range  of  vats  ;  if  it  is  of  a  pale  straw  color,  the  quantity 
produced  will  not  be  so  abundant,  but  it  will  be  of  a  superior  quality 
than  when  the  color  is  of  a  deeper  yellow  tinge.  The  color  of  the 
liquid  after  fermentation,  and  when  it  is  drawn  off,  is  always  more  or 
less  of  a  deep  yellow.  It  is  allowed  to  remain  some  little  time,  then 
the  water,  while  still  warm,  is  beaten  by  twelve  naked  men  armed  with 
long  bamboos.  While  this  is  going  on,  the  higher  range  of  vats  is 
being  emptied  and  cleared  for  another  supply  of  the  plants,  seventeen 
workmen  being  employed  in  cleaning  one  vat.  The  liquid  is  beaten 
for  two  or  three  hours,  and  gradually  becomes  a  pale  green  color,  and 
the  indigo  forms  into  small  flakes  ;  it  is  allowed  to  remain  half  an  hour, 
and  the  water  is  then  turned  off  gently,  corks  placed  at  different  levels 
in  the  vats,  being  one  by  one  withdrawn.  The  water  returns  to  the 
river,  and  the  deposit,  which  resembles  a  thin  scum,  is  carried  through 
a  trough  into  a  deep  trench.  By  means  of  a  hand-putpp,  it  is  then 
brought  up  and  boiled  for  a  short  time  in  order  to  prevent  a  second 
fermentation — which  would  cause  it  to  turn  black  and  be  spoiled.  It 
is  allowed  to  remain  about  twenty  hours,  and  then  the  boiling  process 
