Amo£t%^7.arm'}    Schweizer's  Reagent  and  Eau  Celeste.  507 
SCHWEIZER'S  REAGENT  AND  "  EAU  CELESTE."  1 
By  H.  Batjbigny. 
"  Eau  celeste/'  is  obtained  by  dissolving  copper  salts  in  ammonia, 
and  contains  salts  of  the  type  CuS04,4NH3  +  H20.  Schweizer's  rea- 
gent is  prepared  by  treating  cupric  hydroxide  with  ammonia,  and 
contains  the  base  CuO,4NH3  4-  4H20,  isolated  by  Malaguti  and  Sar- 
zeau.  Both  solutions  deposit  cupric  hydroxide  when  largely  diluted. 
"Eau  celeste/'  contains  salts  of  the  base  which  exists  in  the  free 
state  in  Schweizer's  reagent.  It  follows  that  solutions  of  basic 
cupric  salts  should  behave  as  mixtures  of  "  eau  celeste"  and 
Schweizer's  reagent,  and  this  is  found  to  be  the  case.  Such  solutions 
dissolve  cellulose  more  readily  the  more  basic  the  salt.  Conversely, 
the  addition  of  an  ammonium  salt  to  Schweizer's  reagent  partially 
converts  it  into  "eau  celeste,"  and  if  the  former  has  previously 
been  saturated  with  cellulose,  the  cellulose  is  precipitated  as  the 
ammonium  salt  is  added.  This  change  is  produced  by  ammonium 
carbonate  and  by  carbonic  anhydride,  and  it  follows,  therefore, 
that  when  Schweizer's  reagent  is  exposed  to  the  air  it  will  form 
cuprammonium  carbonate,  and  will  eventually  be  converted  into 
"eau  celeste." 
The  old  method  of  preparing  Schweizer's  reagent  by  dissolving 
copper  in  ammonia  in  presence  of  air,  is  defective,  since  it  does  not 
avoid  the  presence  of  carbonic  anhydride,  and  hence  gives  a  product 
with  diminished  solvent  powers.  Potassium  sulphate  and  sodium 
chloride  are  not  decomposed  by  ammonia  nor  by  the  cuprammo- 
nium base,  and  therefore  they  do  not  affect  the  properties  of 
Schweizer's  reagent.  The  addition  of  potassium  or  sodium  hy- 
droxide to  "  eau  celeste"  produces  a  liquid  which  is  capable  of  dissolv- 
ing cellulose. 
The  best  method  of  preparing  Schweizer's  reagent  is  to  precipitate 
a  solution  of  copper  sulphate  with  the  calculated  quantity  of  soda  and 
dissolve  the  hydroxide  in  ammonia. 
There  can  be  little  doubt  that  the  Schweizer's  reagent  distributed 
over  vines,  as  a  preventative  of  mildew,  will  be  rapidly  transformed 
into  "  eau  celeste,"  which  is  the  actual  preservative.  The  more  easily 
p  r  i  :  "  eau  celeste"  can,  therefore,  be  used  for  this  purpose  instead 
of  the  Schweizer's  reagent. 
1  Compt.  rend,  civ,  1616-1618. — Reprinted  from  Jour.  Chem.  Soc,  Sept.  1887. 
