PREPARATION,  PROPERTIES  AND  COMPOSITION  OF  EMETIA.  309 
sorb  oxygen  from  the  air.  Caustic  ammonia  is  not  a  good  sol- 
vent, yet  ammoniacal  water  retains  a  portion  of  it.  Caustic  lime 
and  magnesia  also,  in  presence  of  moisture,  favor  its  oxidation, 
and  give  it  a  saffron  color. 
Chlorohydric,  sulphuric,  phosphoric  and  acetic  acids  easily  sat- 
urate emetia,  producing  salts,  which  are  all  uncrystallizable,  and 
very  soluble  in  water. 
iN'itric  acid,  on  the  contrary,  forms  a  salt  but  slightly  soluble, 
by  double  decomposition  between  a  soluble  salt  of  emetia  and 
nitrate  of  potassa.  The  precipitate,  at  first  bulky,  soon  agglu- 
tinates into  a  brown  mass.  It  is  uncrystallizable,  and  requires 
100  parts  of  water  for  solution. 
The  insolubility  of  its  nitrate  forms  the  most  distinctive 
chemical  character  of  emetia,  urea  being  the  only  other  base 
which  has  the  same  characteristic. 
Tannin  precipitates  emetia  abundantly  in  aqueous,  alcoholic 
or  saline  solutions. 
loduretted  iodide  of  potassium  also  precipitates  it,  and  bichlo- 
ride of  mercury  and  iodohydrogyrate  of  potassium  form  white 
compounds  insoluble  in  water,  but  soluble  in  alcohol. 
The  platinum  chloride  double  salt,  however,  is  soluble  in  water 
but  not  in  alcohol. 
Emetia  is  also  precipitated  from  its  salts  by  molybdate  of  am- 
monia. 
Composition.  In  1823,  Pelletier  and  Dumas  stated  the  com- 
position of  emetia  per  cent,  to  be  carbon  64-57,  nitrogen  4-30, 
hydrogen  7-77,  oxygen  22*95. 
These  numbers  accord  with  the  formula,  C^°  H^^  NO^ 
But  the  capacity  of  saturation  had  not  then  been  determined. 
M.  Lefort,  by  careful  experiments  with  very  pure  emetia,  has 
made  the  sulphate  and  chlorohydrate  neutral,  and  dried  them  at 
100  F. 
a.  Sulphate  of  Emetia.    I.  0*913  grm.  of  the  salt  gave  0*0711 
of  sulphuric  acid,  or  7*79  per  cent. 
II.  0*563  grm.  of  the  salt  gave  0*042 
of  sulphuric  acid,  or  7*31  per  cent. 
The  formula  Q''  W  W  0^'  +  SO'  requires  6*60  of  acid  per 
cent. 
