2 1 2  Determination  of  Pyrophosphoric  A cid.   { A%Jp°rln;  wt'm' 
I  do  not  advise  boiling.  There  is  no  necessity  for  it.  When  the  salt  is 
dissolved,  add  10  c.c.  of  a  10  per  cent,  solution  of  potassium  or  sodium 
hydrate  ;  stir  and  filter,  after  a  little  while,  into  a  25  c.c.  graduate.  You  will 
obtain  between  12  and  15  c.c.  colorless  filtrate.  (Perforate  the  filter,  and  sub- 
mit the  mixture  of  the  salt,  and  the  potassium  or  sodium  hydrate  solution  to  a 
somewhat  longer  contact  if  not  colorless.) 
Add  five  (5)  c.c.  of  a  10  per  cent,  ammonium  chloride  solution,  and  drop  by 
drop,  from  a  pipette,  from  1  to  2  c.c.  of  a  10  per  cent,  magnesium  sulphate 
solution.  Shake  the  graduate  slowly  as  long  as  the  precipitate,  that  forms, 
redissolves.    Do  not  stir  vigorously. 
In  this  way,  orthophosphates  of  the  alkalies  can  be  separated  from 
pyrophosphates,  a  similar  manner  of  separating  as  is  in  use  in  the 
separation  of  narcotine  from  morphine,  in  opium  assaying,  accord- 
ing to  the  process  of  Dieterich  {Helfenberger  Annalen).  Ortho- 
phosphate  of  ammonia  and  magnesia  forms  later,  if  present,  and 
sinks  to  the  bottom  of  the  graduate,  as  a  distinctly  different  micro- 
crystalline  substance. 
When  the  filtrate  remains  clear,  no  orthophosphate  is  present. 
These  proportions  of  ammonium  chloride  and  magnesium  sulphate, 
and  the  conditions  under  which  the  reactions  took  place,  were  found 
favorable  for  the  determination  of  alkali  pyrophosphates  in  six 
commercial  samples  of  different  manufacturing  companies.1 
If  a  precipitate  has  formed,  it  must  be  collected  on  a  small  filter, 
washed  and  dissolved  on  the  filter  in  dilute  nitric  acid  ;  the  acid 
solution  of  it  has  to  be  made  slightly  alkaline  with  ammonia  water; 
the  precipitate  that  hereby  forms  has  to  be  redissolved  in  dilute 
acetic  acid,  and  this  solution  has  to  be  tested  for  orthophosphoric 
acid  with  a  5  per  cent,  silver  nitrate  solution.  A  canary  yellow 
precipitate  indicates  the  presence  of  orthophosphates. 
(10)  Where  the  text  of  the  U.  S.  P.  reads  : 
"  If  a  portion  of  the  filtrate  be  acidulated  with  acetic  acid  and  heated  to 
boiling," 
it  should  read,  according  to  the  proposition  in  this  paper : 
"  If  a  portion  of  the  filtrate  from  a  precipitate,  if  any,  is  formed  by  the  addi- 
tion of  the  ammonium  chloride  and  magnesium  sulphate  solution,  or  from  the 
colorless  filtrate  mixed  with  ammonium  chloride  and  magnesium  sulphate,  if 
no  precipitate  is  formed  .  .  .  ." 
xT>r.  Stieglitz  detected,  by  taking  much  less  magnesium  sulphate,  one  (1) 
part  orthophosphate  in  nine  (9)  parts  pyrophosphate. 
