Ac,Ap°riir'  i^ilrm'  )    Use  °f  bacteria  in  Preparation  of  Indigo.  275 
THE  USE  OF  BACTERIA  IN  THE  PREPARATION  OF 
NATURAL  INDIGO.1 
We  have  had  occasion  to  refer  to  the  promising  work  now  in 
progress  in  India,  to  establish  upon  a  genuine  scientific  basis  the 
treatment  of  the  indigo  plant,  for  the  transformation  of  the  indican 
present  into  indigo.  The  advance  thus  far  made  by  those  in  charge 
of  this  important  investigation,  Mr.  Hutchinson,  the  bacteriologist, 
and  Mr.  Davies,  the  chemist,  is  outlined  in  a  recent  bulletin  of  the 
Pusa  Research  Institute,  and  is  here  briefly  summarized : 
The  possibility  of  bacterial  action  was  suggested  by  three  facts. 
Firstly,  the  gas  produced  during  the  process  of  fermentation  in  the 
steeping  vat  varies  in  quantity  and  composition ;  secondly,  chemical 
decomposition  commences  near  the  walls  of  the  vat,  and  then  spreads 
inwards,  this  suggesting  that  the  presence  of  bacteria  on  the  walls 
has  something  to  do  with  the  change ;  and,  thirdly,  there  is  a  curious 
divergence  in  the  yield,  not  only  between  different  factories,  but 
between  vats  of  the  same  factory  worked  under  apparently  identical 
conditions,  and  in  particular,  when  a  new  vat  is  brought  into  use 
it  takes  some  days  for  it  to  reach  the  normal  yield  of  the  factory. 
These  observations  suggested  that  the  theory  of  transformation 
so  far  accepted,  by  which  the  main  credit  for  the  change  was  given 
to  a  constituent  in  the  plant  itself,  was  incomplete.  The  conversion 
of  indican,  the  crude  form  of  the  dye,  into  indoxyl — which  is  sub- 
sequently converted  into  indigo  by  oxidation — appeared  to  depend 
in  part  on  outside  agencies,  and  laboratory  researches  showed  this 
to  be  the  case.  It  has  now  been  established  that  bacterial  action 
plays  a  considerable  part  in  the  process  of  change,  being  in  fact 
essential  to  the  extraction  of  the  maximum  yield  of  indigo.  This 
is  a  discovery  of  great  potential  importance,  for  it  at  once  supplies 
an  explanation  of,  and  promises  a  remedy  to,  the  extraordinary 
differences  in  yield  which  occur  in  adjacent  factories.  In  Bihar,  for 
example,  the  variations  are  from  one  to  several  hundred  per  cent., 
and  no  satisfactory  reason  for  their  occurrence  was  previously 
advanced.  It  now  appears  to  be  certain  that  the  high-yielding  vats 
are  equipped  with  a  full  stock  of  beneficial  bacteria,  while  the  low 
yielders  are  either  inadequately  stocked  with  these  or  contain 
actively  hostile  bacteria.    Mr.  Hutchinson  has  isolated  the  adverse 
From  The  Chemical  Engineer. 
