A  cold  method  for  bleaching  loose  cotton  has  been  proposed
wherein  the  cotton  is  first  treated  in  a  suitable  machine  so  that
cold  water  is  forced  through  the  mass  under  considerable  pressure;
then  a  cold  solution  of  bleaching  powder  is  circulated  through
the  cotton,  and  subsequently  dilute  acid,  followed  by  a  thorough
washing  and  soaping.     This  method  is  said  to  leave  the  cotton
almost  unimpaired  as  to  its  spinning  qualities.     Such  a  process  is
attaining  considerable  practical  value  for  the  spinning  of  filling
cops  from  bleached  stock.
Loose  cotton,  however,  is  largely  bleached  for  use  as  medicinal
absorbent  cotton.  The  object  in  view  in  this  case  is  not  only  to
obtain  a  white  and  pure  fibre,  but  also  to  make  it  highly  absorbent
of  liquids.  In  fact,  the  purpose  is  not  so  much  to  bleach  the
cotton  in  the  sense  of  destroying  the  color,  as  to  remove  all
impurities  from  the  fibre  which  may  in  any  manner  interfere  with
its  ready  absorption  of  liquids.  Hence,  the  chief  operation  is  a


52  DYEING   AND    TEXTILE   CHEMISTRY.
very  thorough  boiling-out  to  remove  perfectly  the  waxy  and
resinous  matters.  For  this  purpose  the  cotton  is  boiled  in  a  com-
paratively strong  solution  of  caustic  soda  under  pressure  for  8  to
10  hours.  After  this  treatment  it  is  bleached  in  the  usual  manner
with  chloride  of  lime  and  sulphuric  acid.  The  quality  of  absorb-
ent cotton  is  tested  by  the  readiness  with  which  it  sinks  in  water.
10.  Bleaching  with  Acetic  Acid.  —  In  some  cases  cotton  is
bleached   with   the   use   of  acetic   rather  than   sulphuric   acid.
