462  Seidlitz  Powders.  {A™cSr,Pi5oam* 
anything  like  this,  and  it  would  be  likely  to  pass  unnoticed  when 
the  powders  were  mixed  for  drinking. 
To  make  practical  tests  for  the  examination  of  seidlitz  powders, 
materials  were  taken  such  as  are  ordinarily  used  in.  the  drug  store, 
and  first  examined  qualitatively  by  the  official  tests. 
The  tartaric  acid  answered  the  official  requirements  with  the 
exception  of  a  slight  cloudiness  with  barium  chloride  test  solution. 
The  ash  amounted  to  -07  per  cent.  The  loss  of  moisture  on  dry- 
ing at  100°  C.  amounted  to  about  -027  per  cent. 
The  sodium  bicarbonate  gave  a  slight  turbidity  with  silver  nitrate 
test  solution,  with  barium  chloride  test  solution,  and  a  slight  colora- 
tion with  hydrogen  sulphide  when  followed  by  ammonia  water. 
The  loss  of  weight  on  heating  at  ioo°  C.  amounted  to  36-58  per 
cent.  The  Pharmacopoeia  gives  about  36*3  per  cent.,  a  98-6  per 
cent,  salt  being  allowed.  The  theoretical  amount  for  a  pure  salt  is 
about  36-88  per  cent. 
The  rochelle  salt  also  proved  to  be  very  pure.  It  showed  a 
slight  coloration  with  hydrogen  sulphide,  and  a  slight  turbidity 
witti  silver  nitrate  test  solution.  The  loss  in  weight  on  heating  at 
100°  C.  amounted  to  about  23-35  Per  cent.  Theoretically,  rochelle 
salt  contains  about  25-52  per  cent,  of  water  of  crystallization. 
The  drying  of  the  salts  was  also  tried  at  a  temperature  of  500 
C,  with  the  object  of  ascertaining  if  the  adhering  moisture  could 
be  estimated  at  that  temperature  without  the  loss  of  water  of 
crystallization,  or,  in  the  case  of  the  bicarbonate  of  soda,  with- 
out decomposition.  It  was  found  that  some  decomposition  did  take 
place,  and,  also,  so  much  time  was  required  and  the  results  so  irreg- 
ular as  to  be  impracticable.  Rochelle  salt  is  somewhat  efflores- 
cent at  the  ordinary  temperature  in  dry  air,  and  sodium  bicarbonate 
is  very  apt  to  decompose.  Having  examined  the  materials  sepa- 
rately as  to  their  quality,  the  sodium  bicarbonate  and  rochelle  salt 
were  mixed  in  the  proportions  directed  by  the  Pharmacopoeia  for 
seidlitz  powders,  for  the  purpose  of  examining  quantitatively. 
As  both  the  constituents  of  seidlitz  "mixture  are  salts  of  alkali 
metals,  they  cannot  be  separated  for  estimation  by  precipitation. 
Nor  do  the  acid  radicals  form  any  insoluble  salts,  so  that  the  only 
practical  way  is  to  take  advantage  of  the  behavior  of  the  com- 
ponents towards  volumetric  solutions  before  and  after  ignition. 
The  experiments  made  lead  to  the  following  suggestions  for  the 
qualitative  and  quantitative  examination  of  seidlitz  mixture : 
