130 
ANALYSIS  OF  PRUSSIC  ACID,  AC. 
VOLUMETRIC  ANALYSIS  OF  PREPARATIONS  CONTAINING 
PRUSSIC  ACID,  OIL  OF  BITTER  ALMONDS,  &c. 
By  W.  H.  Pile,  M.  D. 
Read  at  the  Pharmaceutical  Meeting  of  the  Philadelphia  College  of  Pharmacy, 
January  7th,  1862. 
Owing  to  the  minute  quantity  of  prussic  acid  in  the  distilled 
waters  containing  that  substance,  it  requires  great  nicety  in  ascer- 
taining the  percentage  strength,  by  the  usual  method  of  precip- 
itating by  nitrate  of  silver,  and  drying  and  weighing  the  resulting 
cyanide  ;  manipulations  which  likewise  occupy  considerable  time. 
Liebig,  to  whom  science  is  so  much  indebted,  devised  an  ex- 
ceedingly ingenious  plan  for  the  same  purpose,  which  is  unex- 
ceptionable in  point  of  accuracy.  But  as  measuring  is  much  more 
rapidly  performed  than  weighing,  it  occurred  to  me  to  reduce 
Liebig's  process  to  a  volumetric  analysis,  and  thus  put  it  in  the 
power  of  the  pharmaceutist  to  ascertain  speedily  and  satisfactorily 
the  medicinal  value  of  several  remedial  preparations,  which  not 
unfrequently  he  is  called  upon  to  dispense,  and  which,  unfortun- 
ately, will  be  found  in  too  many  instances  either  entirely  inert 
or  most  sadly  deteriorated  in  efficiency. 
For  this  purpose  I  prepared  a  test  solution  of  nitrate  of  silver 
of  such  strength,  that  for  every  measure  of  it  employed  in  the 
analysis,  a  quantity  of  prussic  acid  would  be  indicated,  showing 
the  proportion  of  one-tenth  of  one  per  cent  in  any  liquid  under 
examination,  and  as  less  than  one-tenth  of  a  measure  of  the  test 
solution  occasions  a  perceptible  change  in  the  appearance  of 
the  liquid,  a  difference  of  one  grain  in  ten  thousand  is  thus 
readily  detected. 
The  rationale  of  the  process  is  as  follows  :  prussic  acid  when 
combined  with  potassa,  forming  cyanide  of  potassium,  has  the 
property  of  rapidly  dissolving  freshly  precipitated  cyanide  of 
silver,  in  such  quantity  that  one  grain  of  anhydrous  prussic  acid 
combined  as  above,  will  hold  in  solution  all  the  cyanide  thrown 
down  from  3-148  grains  of  nitrate  of  silver,  and  forming  with  it 
the  soluble  double  cyanide  of  silver  and  potassium.  Now  if  more 
than  that  quantity  of  silver  be  added,  the  excess  being  precipi- 
tated as  oxide,  and  remaining  undissolved,  renders  the  liquid 
turbid.  The  quantity  of  the  test  solution  employed  is  thus 
easily  determined,  and  the  amount  of  prussic  acid  directly  indi- 
cated. 
