AmAP0rUii;Srm"}  Determination  of  Pyrophosphoric  Acid.  211 
(4)  The  prescription  of  the  U.  S.  P.  which  is  referred  to  here 
(p.  193)  is  all  very  well  for  an  expert  analyst.  But  it  does  not 
work  well  with  less  experienced  operators.  The  writer  received, 
lately,  official  complaints  from  manufacturers  of  pyrophosphates, 
that  they  objected  to  the  application  of  the  U.  S.  P.  test  for  purity 
of  their  article,  i.  e.,  absence  of  orthophosphates. 
(5)  I  agreed.  But  they  seem  not  to  have  read  an  article  by  my 
colleague,  Prof.  Dr.  Julius  Stieglitz,  on  the  previous  Pharma- 
copoeia, or  it  has  escaped  their  memory  [Am.  J.  P/i.,  1 891,  p.  585). 
(6)  The  reader  is  requested,  to  prevent  misunderstanding,  to 
operate  literally,  as  is  here  prescribed.  This  will  furnish  proof 
to  any  unbiased  mind  that  it  is  better  to  make  the  determination  of 
pyrophosphoric  acid  in  the  presence  of  orthophosphoric  acid, 
according  to  Fresenius,  than  according  to  the  U.  S.  P. 
(7)  "  If  1  gm.  of  the  salt  be  boiled  with  ioc.c.  of  potassium  hydrate  T.S.,  a  red- 
dish-brown precipitate  will  be  produced,  and  if  the  colorless  filtrate  from  this  pre- 
cipitate be  strongly  acidulated  with  hydrochloric  acid,  then  magnesia  mixture 
added,  and  subsequently  a  slight  excess  of  ammonia  water,  no  precipitate 
should  be  produced." — U.  S.  P.,  p.  193. 
(Italics  are  mine.) 
(8)  This  somewhat  vague  prescription  (see  italics)  is  a  source  of 
fatal  errors  to  an  operator  of  limited  experience  in  analytical 
chemistry. 
Tzvo  (2)  c.c.  magnesia  mixture  seem  to  be  a  fair  proportion  for  the 
colorless  filtrate,  and  five  (5)  drops  of  ammonia  water  furnish  the 
slight  excess  of  the  latter. 
In  five  commercial  samples,  used  for  this  paper,  I  did  not  obtain 
an  orthophosphoric  acid  reaction  with  two  (2)  c.c.  magnesia  mixture 
and  five  (5)  drops  of  ammonia  water.  Orthopliosphoric  acid  was, 
however,  largely  present  in  all  the  samples,  as  is  shown  below, 
where  other  results  are  recorded,  obtained  from  the  same  samples. 
I  found  that  many  iron  pyrophosphates  in  the  market  are  only 
pyrophosphates  in  name  ;  that  pyrophosphoric  acid,  for  economy's 
sake,  perhaps,  is  only  to  be  found  on  their  labels. 
(9)  The  confusion  of  the  quoted  vague  prescription  of  the 
U.  S.  P.  is  to  be  avoided  as  follows  (to  which  Dr.  Stieglitz  called 
attention  already  years  ago)  : 
Dissolve  1  gm.  of  the  salt  under  examination,  for  the  determination  of  pvro- 
phosphoric  acid,  in  ten  (10)  c.c.  of  water. 
