m  PlTROPHOSPlIORIC  ACID. 
Ml 
ON  PYROPHOSPHORXC  ACID. 
By  Dr.  J,  H.  Gladstone. 
According  to  Graham's  original  view  of  the  constitution  of 
this  acid,  when  regarded  as  2HO,P05,  it  was  believed  to  be  a 
bibasic  acid.  Since  the  atomic  weight  of  oxygen  has  been 
-doubled,  its  formula  is  written  2H2O^P205=P2H407,  and  it 
becomes  a  tetrabasic  acid.  The  correctness  of  the  latter  view 
receives  support  from  the  existence  of  amides  containing  one, 
two,  and  even  three  molecules  of  NH2  in  the  place  of  HO.  The 
present  paper  treats  of  some  normal  pyrophosphates,  and  cer- 
tain allotropic  modifications  of  these  salts,  and  indicates  the  con- 
stitution of  the  acid  as  deduced  from  several  modes  of  forma^ 
tion.  The  author  confirms  Schwartzenberg's  analysis  of  the 
ferric  pyrophosphate,  P,2fe407-f  3H20,*  and  suggests  the  exist- 
ence of  a  soluble  double  salt  P2Na2fe2Or  The  cupric  salt  was 
found  t-o  have  a  similar  composition,  but  contained  only  two 
atoms  of  water.  Dr.  Gladstone  mentioned  some  remarkable 
facts  tending  to  establish  the  existence  of  an  allotropic  ferric 
pyrophosphate.  Thus,  if  a  solution  of  sodium  pyrophosphate 
be  mixed  with  a  large  excess  of  sulphuric  acid,  and  ferric  chlo- 
ride then  added,  there  is  no  precipitate  in  the  cold ;  but,  on  heat- 
ing, a  white  flocculent  compound  is  formed,  which  differs  from 
the  ordinary  modification  of  that  substance  by  being  insoluble 
either  in  dilute  mineral  acids,  ferric  chloride,  or  in  alkaline 
pyrophosphates.  A  quantity  of  this  substance  was  prepared 
and  analyzed.  Its  composition  was  found  to  be  identical  with 
that  previously  recognized — viz.,  P2fe407,3H?0.  It  is  proposed 
to  use  this  reaction  as  a  test  for  the  acid  in  question.  Similar 
results  were  observed  in  the  case  of  copper.  Regarding  the 
modes  of  preparation,  it  was  stated  that  the  pyrophosphates  had 
hitherto  been  obtained  by  the  action  of  heat  upon  the  ortho- 
phosphates,  but  Dr.  Gladstone  succeeded  in  producing  them  by 
dissolving  phosphoric  anhydride  in  an  alcoholic  solution  of 
hydrate  of  potassium  or  other  alkaline  base ;  or,  if  the  oxy- 
chloridc  of  phosphorus  be  dropped  into  a  strong  aqueous  solution 
of  the  same  hydrate,  the  product  was  identical.    That  this 
*  Ferviwm  (fe)  ==  18'66.  (Williamson.) 
