^'^'InSl'im^'''^'}    Estimation  and  Separation  of  Metals.  421 
colors  mastic  and  sandarach  bright  yellow;  elemi,  a  dirty  yellow. 
Aqueous  soda  dissolves  shellac  readily;  colophony  with  difficulty, 
but  is  with(>ut  solvent  action  on  the  others.  Colophony  dissolves 
readily  in  strong  ammonia ;  mastic,  sandarach,  and  copal  swell  up 
before  dissolving  ;  whilst  amber,  dammar,  shellac,  and  elemi  remain 
unchanged. 
ESTIMATION  AND  SEPARATION  OF  METALS  BY 
MEANS  OF  SODIUM  PYROPHOSPHATE.^ 
By  G.  VORTMANN. 
The  behavior  of  metallic  salts  towards  sodium  pyrophosphate  and 
acetic  acid  can  be  employed  as  a  means  of  separating  the  metals,  and 
the  pyrophosphates  thus  obtained,  being  insoluble  in  water,  dilute 
acetic  acid,  and  solutions  of  ammonium  salts,  can  be  made  use  of  for 
quantitative  determinations. 
Copper  salts  give  with  sodium  pyrophosphate  a  bright  blue  preci- 
pitate, soluble  in  excess  of  the  reagent ;  on  adding  acetic  acid,  a  bright 
blue  crystalline  precipitate  is  obtained,  the  precipitation  is,  however, 
incomplete,  and  can  be  entirely  prevented  by  the  addition  of  sodium 
tartrate  or  sodium  thiosulphate. 
Cadmium  salts  give  a  precipitate  soluble  in  excess.  Acetic  acid 
reprecipitates  the  salt  almost  completely  even  in  the  cold ;  by  evapo- 
rating to  dryness  and  digesting  the  residue  with  water,  reprecipitation 
is  complete.  The  addition  of  sodium  tartrate  or  thiosulphate  does  not 
hinder  precipitation. 
Manganese  salts  yield  a  precipitate,  soluble  in  excess,  but  complete- 
ly reprecipitated  by  acetic  acid  ;  sodium  tartrate  does  not  prevent  the 
precipitation. 
Zinc  salts  behave  similarly,  but  reprecipitation  is  complete  only  when 
the  solution  is  evaporated  to  dryness  and  the  residue  taken  up  with 
water  ;  sodium  tartrate  retards  reprecipitation. 
Cobalt  salts  give  a  gelatinous  precipitate,  soluble  in  excess  ;  on 
shaking  or  heating  gently,  the  solution  becomes  gelatinous  but  not  if 
sodium  tartrate  is  added.  Acetic  acid  reprecipitates  the  cobalt  salt. 
Presence  of  sodium  tartrate  does  not  prevent  reprecipitation. 
i/owr.  Chem.  Soc,  1888,  p.  755;  Berichte,  1888,  p.  1103. 
