464 
Seidlitz  Powders. 
( Am.  Jour.  Pharm. 
I     October,  1900. 
tralized  by  normal  potassium  hydrate  volumetric  solution,  it 
should  be  found  to  require  not  more  than  5-96  c.c.  of  sulphuric  acid 
volumetric  solution  to  produce  a  neutral  solution  (corresponding  to 
25  per  cent,  of  sodium  bicarbonate,  each  cubic  centimetre  being 
the  equivalent  of  -08385  gramme). 
If  2  grammes  of  the  mixture  be  again  taken,  this  thoroughly 
ignited  in  a  platinum  crucible,  the  crucible  with  ash  adhering  boiled 
in  distilled  water  until  the  ash  is  dissolved,  then  normal  sulphuric 
acid  volumetric  solution  added  in  excess  as  before,  boiled,  phenol- 
phtalein  added,  and  the  excess  of  acid  neutralized  with  normal 
potassium  hydrate  volumetric  solution,  the  number  of  cubic  centi- 
metres of  acid  found  to  be  required,  minus  5-96  (the  amount 
required  for  the  sodium  bicarbonate  alone),  should  leave  not  less 
than  10*65  c.c.  (corresponding  to  75  per  cent,  of  rochelle  salt,  each 
cubic  centimetre  being  the  equivalent  of  -140755  gramme). 
The  Pharmacopceial  blue  powder  containing  2-583  grammes  of 
sodium  bicarbonate  would  require,  theoretically,  2-305  grammes  of 
tartaric  acid  to  exactly  neutralize  83-85  (NaHC03)  :  74-82  (^H2C4- 
H406)  :  :  2-583  :  2-305,  while  the  amount  given  is  2-25  grammes, 
leaving  a  deficiency  of  nearly  1  grainr  It  might  be  claimed  that,  as 
the  sodium  bicarbonate  of  the  Pharmacopoeia  is  allowed  to  be  of 
only  98-6  purity,  this  would  make  an  acid  solution.  Further 
calculation  showed  that  it  does  not.  If  a  100  per  cent,  pure  sodium 
bicarbonate  required  2-305  grammes  of  tartaric  acid,  a  98-6  per 
cent,  salt  would  require  2-273  grammes,  100  :  98-6  :  :  2-305  :  2-273. 
These  figures  are  for  a  tartaric  acid  of  absolute  purity,  whereas 
it  is  most  likely  to  be  at  least  a  fraction  of  1  per  cent,  short  of  this, 
while  there  is  good  reason  to  believe  that  most  of  the  sodium  bicar- 
bonate now  on  the  market  comes  well  within  the  official  require- 
ments. The  official  quantity  of  tartaric  acid,  if  absolutely  pure, 
would  only  be  equal  to  a  sodium  bicarbonate  of  97-6  per  cent, 
purity,  2  583  (official  quantity)  :  2-5215  (equivalent  quantity)  :  : 
100  :  97-6. 
The  tartaric  acid  was  estimated  by  the  official  process  with  potas- 
sium hydrate,  but  to  avoid  precipitation  of  potassium  bitartrate  it  is 
recommended  to  titrate  in  hot  solutions. 
The  methods  for  the  examination  of  seidlitz  powders  having  been 
described,  the  results  upon  six  samples  are  given. 
The  blue  and  white  powders  are  considered  under  separate  head- 
