CONVERSION  OF  THE  PHOSPHORIC  ACIDS. 
387 
yellow.  The  solution,  it  appears,  contains  pyrophosphoric  acid, 
and  is  not  perceptibly  changed  on  continuing  to  boil  for  several 
hours  more. 
The  syrupy  liquid  contained  in  bottles  filled  with  glacial  phos- 
phoric acid,  after  having  absorbed  some  moisture,  consists  at  first 
of  the  mono-  and  deutohydrate,  dissolved  in  water  ;  heated  to 
boiling,  it  changes  very  slowly  into  the  bibasic  acid.  As  the 
conversion  proceeded  much  slower  than  in  the  former  instance, 
experiments  were  made  with  a  very  dilute  solution. 
This  diluted  solution,  containing  about  a  drachm  of  the  glacial 
acid  in  8  or  10  fluid  ounces  of  water,  was  heated  to  boiling  and 
kept  at  this  temperature  ;  in  about  twenty  minutes  it  had  lost 
the  property  of  coagulating  albumen  ;  but  previous  to  this,  the 
precipitate  with  silver  was  perceptibly  yellow,  though  not  quite 
as  deep  colored  as  from  the  common  phosphate  of  soda. 
This  precipitate  had  not  become  of  a  deeper  yellow  after  the 
liquid  ceased  to  coagulate  albumen,  and  if  the  boiling  was  con- 
tinued for  several  hours,  little  change  could  be  perceived.  It 
was  evident  that  the  solution  contained  some  terhydrate  and 
deutohydrate  mixed.  Experiments  were  now  made  with  the 
same  solutions,  the  strong,  syrupy,  and  dilute,  at  temperatures 
between  110  and  200^  F.  In  all  instances  the  result  was  simi- 
lar to  that  just  described,  with  the  exception  that  generally  a 
longer  time  was  required  to  alter  the  monohydrate,  the  lower 
the  temperature  was  to  which  the  solution  was  exposed.  Now, 
too,  the  strong  solutions  afi'orded  no  evidence  of  the  presence  of 
the  terhydrate  after  the  monohydrate  had  disappeared,  while 
the  weak  solution,  on  the  contrary,  contained  terhydrate,  as 
was  shown  by  the  color  of  its  silver  precipitate. 
If  phosphorus  is  oxidized  by  nitric  acid,  the  solution  contains 
common  phosphoric  acid,  which,  after  evaporation,  may  by  heat 
be  converted  into  the  deuto-  and  monohydrate.  If  the  mono- 
hydrate is  now  dissolved  in  diluted  nitric  acid  and  heated,  it 
will  lose  its  property  of  coagulating  albumen,  and  will  produce 
a  yellow  precipitate  with  silver  salts,  identical  in  color  with  that 
obtained  from  the  common  phosphate  of  soda.  This  change  in 
the  presence  of  nitric  acid  does  not  appear  to  be  unaffected  by 
the  density  of  the  solution;  but,  as  before,  a  more  dilute  solution 
is  more  readily  converted  into  the  tribasic  acid  than  a  concen- 
