NEW  PROCESS  FOR  INDIGO  DYEING. 
269 
of  attacking  the  metal.  Thus,  a  platinum  crucible  becomes 
sensibly  impure  after  prolonged  ignition  at  a  high  temperature, 
bedded  in  commercial  magnesia.  On  the  other  hand,  I  have  kept 
a  platinum  crucible  at  a  constant  weight  to  the  tenth  of  a  milli- 
gramme over  a  series  of  intense  ignitions,  when  the  precaution 
has  been  taken  to  bed  it  in  chemically  pure  magnesia. — Chem. 
News,  March  30,  1866.' 
NEW  PROCESS  FOR  INDIGO  DYEING. 
By  M.  J.  0.  Leuchs. 
Before  it  can  be  used  for  dyeing,  indigo  must  be  rendered 
soluble  in  alkaline  and  caustic  solutions  by  being  treated  by  a 
reducing  body ;  by  this  reaction  indigo  loses  its  color,  but  after 
being  fixed  on  stuff  and  exposed  to  the  air  it  absorbs  fresh  oxy- 
gen and  returns  to  its  original  color.  This  process,  theoretically 
so  simple,  is  practically  complicated  by  serious  difficulties,  and 
requires,  on  the  part  of  the  dyer,  much  practice  and  great  dex- 
terity. Thus,  for  instance,  with  indigo  reduced  by  fermentation 
with  vegetable  matters  in  a  caustic  solution,  the  various  acids 
produced  during  the  fermentation  combine  with  the  alkali,  the 
liquid  soon  ceases  to  be  caustic,  and  loses  the  property  of  dissolv- 
ing the  reduced  indigo.  To  remedy  this  a  fresh  quantity  of 
alkali  (soda,  potash,  or  lime,)  must  be  added  from  time  to  time ; 
but  should  an  insufficient  quantity  be  added,  a  portion  of  the 
reduced  indigo  remains  undissolved,  and  soon  decomposes  under 
the  fermenting  matter.  If,  on  the  contrary,  an  excess  of  alkali 
be  added,  a  certain  quantity  of  white  indigo  is  lost  by  its  com- 
bining with  potash,  and  forming  an  insoluble  product. 
According  to  M.  Leuchs  (of  Nuremburg),  all  these  objections  , 
are  obviated  by  effecting  the  change  from  blue  to  white  indigo  by 
pectine.  Pectine  exists  in  considerable  quantities  in  the  turnips 
of  different  species,  in  pumpkins,  melons,  &c;  it  may  be  extracted 
from  these  fruits,  or  they  may  even  be  directly  used  to  reduce 
indigo.  The  most  simple  process  consists  in  heating  45  or  50 
kilogrammes  of  the  caustic  ley  to  75°  C,  adding  half  a  kilogramme 
of  well  pulverized  indigo,  then  suspending  in  the  vat  a  kind  of 
basket  of  iron  wire,  containing  from  8  to  10  kilogrammes  of  fresh 
