INDIGO  BLUE.     See  Ikdisotin.
INDIGO  DYE.  There  are  two  methods  of
preparing  solutions  of  indigo  for  dyeing. — 1.
By  deoxidising  it,  and  then  dissolving  it  in
alkaline  menstrua. — 2.  By  dissolving  it  in  sul-
phuric acid.  The  former  method  is  used  in
preparing  the  ordinary  indigo  vat  of  the
dyers.
"  1.  o.  (Cold  tat.)  Take  of  indigo,  in  fine
powder,  1  lb. ;  green  copperas  (clean  cryst.),
2^  to  3  lbs. ;  newly  slaked  lime,  3}  to  4  lbs. ;
triturate  the  powdered  indigo  with  a  little
water  or  an  alkaline  lye,  then  mix  it  with  some
hot  water,  add  the  lime,  and  again  well  mix,
after  which  stir  in  the  solution  of  copperas,
and  agitate  the  whole  thoroughly  at  intervals
for  24  hours.  A  little  caustic  potassa  or  soda
is  frequently  added,  and  a  corresponding  por-
tion of  lime  omitted.  For  use,  a  portion  of
this  '  preparation  vat '  is  ladled  into  the
•dyeing  vat,'  as  wanted.  After  being  em-
ployed for  some  time,  the  vat  must  be  re-
freshed with  a  little  more  copperas  and  fresh-
sliiked  lime,  when  the  sediment  must  be  well
stirred  up,  and  the  whole  thoroughly  mixed
together.  This  is  the  common  vat  for
cotton.
i.  (Potash  tat.)  Take  indigo,  in  fine
powder,  12  lbs. ;  madder,  8  lbs. ;  bran,  9  lbs.  j
'potash,*  24  lbs.;  water  at  125°  Fahr.,  120
cubic  feet ;  mix  well ;  at  the  end  of  about  36
hours  add  14  lbs.  more  potash,  and  after  10  or
12  hours  longer  further  add  10  lbs.  of  potash,
and  rouse  the  whole  up  well ;  as  soon  as  the
fermentation  and  reduction  of  the  indigo  are
well  developed,  which  generally  takes  place  in
about  72  hours,  add  a  little  fresh-slaked  lime.
