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ALTERATION  OP  TINCTURE  OF  IODINE. 
PREPARATION  OF  PURE  NITRATE  OF  SILVER. 
By  M.  Lienau. 
Attack  cupreous  silver  containing  copper  by  nitric  acid  ;  to  the 
solution,  sufficiently  concentrated,  add  chlorine  water,  freshly 
prepared,  which  precipitates  the  silver  only.  Then  wash  the 
precipitate  in  chlorine  water,  which  prevents  the  chloride  of  sil- 
ver from  decomposing  under  the  influence  of  light,  and  renders  it 
more  speedily  soluble  in  solution  of  ammonia  ;  when  well  washed, 
dissolve  it  in  that  liquid,  and  plunge  into  the  solution  a  well 
cleaned  copper-wire.  As  the  copper  dissolves,  the  silver  is  pre- 
cipitated, and  is  deposited  as  a  brown  powder ;  the  operation  is 
at  an  end  when  the  wire  preserves  its  brightness  after  being 
washed  in  water. 
To  render  the  precipitated  silver  perfectly  pure,  it  is  only 
necessary  to  wash  it  in  ammoniacal  water. — Ibid,  from  Archiv 
ddr  Pharm. 
ON  THE  ALTERATION  OF  TINCTURE  OF  IODINE,  AND  THE 
MEANS  OF  PREVENTING  IT. 
By  M.  Dropet. 
It  is  known  that  tincture  of  iodine  does  not  long  preserve  its 
color,  a  portion  of  the  iodine  changing  to  hydriodic  acid.  M. 
Dropet  endeavors  to  show  that  the  hydrogen  necessary  for  the 
reaction  comes  from  the  water,  and  not,  as  is  supposed  by  other 
chemists,  from  the  alcohol.  Among  other  experiments,  he  has 
shown  that  a  tincture  prepared  with  almost  absolute  alcohol,  34 
centigrammes  out  of  3  grammes  of  iodine,  were  in  eighteen 
months  transformed  into  hydriodic  acid.  Another  tincture, 
prepared  with  the  same  proportion  of  alcohol  at  95°,  lost  41 
centigrammes;  and  a  third,  with  alcohol  at  86°,  67  centigrammes. 
These  tinctures  were  preserved  together  in  a  dimly-lighted 
cupboard.  M.  Dropet  concludes  that  in  making  tincture  of 
iodine  it  would  be  better,  for  two  reasons,  to  replace  the  alcohol 
at  86°  by  that  of  95Q.  In  the  first  place,  the  tincture  keeps 
better ;  in  the  second,  it  is  made  more  quickly,  since  iodine  is 
much  more  soluble  in  concentrated  than  in  weak  alcohol. — Chem. 
News,  London,  May  3,  1862,  from  Repertoire  de  Pharmacie. 
