68  Decomposition  of  Salts  by  Water.  {^■"•FLbiriyt''"'' 
ceases  to  decompose  the  neutral  salt  at  12°  C,  will  again  decompose 
it  and  color  it  yellow  on  raising  the  temperature.  The  presence  of 
another  acid  in  the  liquid  makes  no  change  in  the  reaction. 
The  second  note  of  Mr.  Ditte  treats  of  the  action  of  water  on  nitrate 
and  subnitrate  of  bismuth  and  chloride  of  antimony. 
At  the  ordinary  temperature,  the  crystals  of  nitrate  of  bismuth 
Bi03,3N05,3HO  are  immediately  decomposed  by  water,  which  be- 
comes strongly  acid  ;  at  the  same  time  a  white  precipitate,  always 
crystalline,  appears.  The  crystals  have  the  formula  Bi03N05  with 
one,  two,  three  or  four  equivalents  of  water,  according  to  the  temper- 
ature. The  decomposition  ceases  as  soon  as  the  proportion  of 
free  acid  is  83  grams  to  the  litre,  and  then  the  nitrate  simply  dis- 
solves. On  the  addition  of  either  water  or  nitric  acid,  the  composi- 
tion of  the  mixture  is  modified,  until  it  again  reaches  that  quantity  of 
free  acid,  which,  if  in  excess,  combines  with  the  subnitrate  to  recon- 
struct the  neutral  salt,  or,  if  insufficient,  decomposes  the  neutral  nitrate 
previously  dissolved.  Successive  additions  of  water  to  an  acid  solution 
of  neutral  nitrate  determine  the  precipitation  of  subnitrate,  and  the 
liquid  returns  always  to  its  limit  of  acidity  until  the  neutral  salt  has 
entirely  disappeared. 
On  heating  a  clear  solution  of  neutral  nitrate,  a  crystalline  precipi- 
tate of  subnitrate  will  be  observed,  which  disappears  on  cooling.  In 
raising  the  temperature  the  limit  of  free  acid  is  augmented,  which  the 
solution  must  have  to  avoid  decomposition  of  the  neutral  salt ;  this  is 
then  decomposed  but,  on  cooling,  the  free  nitric  acid  and  subnitrate 
again  combine  and  the  precipitate  disappears.  The  subnitrate  of  bis- 
muth Bi03,N0-,H0,  is  also  decomposed  by  water  into  free  acid  and 
an  amorphous  more  basic  salt.  The  decomposition  is  slow  in  the 
cold,  but  at  100°  C.  the  water  decomposes  it  until  it  contains  about  4 
to  5  grams  free  acid  per  litre,  finally  forming  the  basic  nitrate  ^BiOg, 
NO5.  Water  of  100°  C,  containing  less  than  4  to  5  grams  of  acid 
per  litre,  becomes  turbid  and  immediately  decomposes  the  subnitrate  ; 
the  liquid  becomes  clear  from  4  to  5  grams,  while  the  free  acid  in  ex- 
cess combines  with  the  sub-salt  2Bi03,NO,  formed,  and  the  nitrate 
Bi03,N0-  appears  again  with  its  crystalline  form  and  its  silvery  lustre. 
In  the  same  manner  the  neutral  salt,  treated  with  water,  yields  at  first 
the  crystalline  subnitrate  Bi03,N05,  which,  when  washed  with  cold 
or  warm  water,  is  transformed  into  a  white  powder,  which  is  a  mixture 
of  the  basic  salts  2Bi03,N05,and  Bi03,N0..    After  a  prolonged  wash- 
