ACTION  OF  BICHLORIDE  OF  TIN  ON  STARCH.  455 
very  dilute,  as  otherwise  the  linen  suffers.  From  the  high  price 
of  oxalic  acid,  therefore,  a  cheap  means  is  wanting,  when  a 
great  quantity  of  such  iron  moulds  is  to  be  destroyed.  A  case 
of  this  kind  once  occurred  to  the  author;  in  which  sulphate  of 
iron  had  been  used  instead  of  potash,  by  which  300  napkins  and 
other  table-linen  all  acquired  a  rusty  yellow  color,  which,  on 
being  washed  with  soap,  instead  of  disappearing,  became  darker ; 
the  sulphate  of  iron  being  decomposed  by  the  soap,  and  oleate 
of  iron  precipitated  upon  the  fibres. 
Immersion  even  for  several  days  in  water  acidulated  with  sul- 
phuric and  muriatic  acids  produced  no  effect,  because  the  oleate 
of  iron  was  not  decomposed.  It  was  here  that  the  ferrocyanide 
of  potassium  did  such  excellent  service.  It  was  added  in  com- 
paratively small  quantity  to  the  water,  acidulated  with  sulphuric 
acid,  and  the  linen  was  then  moved  about  in  the  fluid.  The 
linen  became  blue.  When  all  the  yellow  had  disappeared,  and 
a  clear  blue  had  made  its  appearance,  the  linen  was  rinsed  and 
treated  with  solution  of  carbonate  of  potash.  Here  the  blue  color 
again  disappeared,  and  with  it  a  great  part  of  the  yellow,  which 
only  remained  in  spots.  These  were  then  very  easily  got  rid  of 
by  dilute  sulphuric  acid  alone. 
The  explanation  of  this  process  is  easy-  By  the  formation 
of  prussian  blue,  the  oleic  acid  is  separated  from  the  oxide  of 
iron.  The  carbonate  of  potash  then  brought  into  action  com- 
bines with  the  oleic  acid,  decomposes  the  prussian  blue,  and  at 
the  same  time  also  dissolves  the  greater  part  of  the  oxide  of  iron, 
so  that  almost  all  the  iron-mould  disappears  from  the  stuff  simul- 
taneously with  the  prussian  blue.  Caustic  lye  does  not  act  in 
the  same  way  :  it  certainly  destroys  the  blue,  but  the  rusty  yel- 
low remains,  because  it  has  not  the  same  solvent  action  upon 
oxide  of  iron  as  carbonate  of  potash.- — Lon.  Chem.  Gf-az.,  July 
1, 1857,  from  Polyt.  Qentralbl. 
ACTION  OF  BICHLORIDE  OF  TIN  ON  STARCH. 
By  M.  H.  De  Payr. 
On  wetting  a  microscopic  slice  of  a  horse-chestnut  with  a  little 
bichloride  of  tin,  the  fecula  is  observed  to  disappear.  This 
