AMFebUi;  m4RM'}    Examination  of  Hydrocyanic  Acid.  69 
AN   EXAMINATION    OF   SOME  SAMPLES  OF  HYDROCYANIC 
ACID.* 
By  A.  Towerzey. 
Some  little  time  since,  at  the  suggestion  of  Mr.  Schacht,  I  submitted 
to  a  careful  examination  the  hydrocyanic  acid  we  were  then  using  in 
his  dispensary.  As  we  half  suspected,  it  proved  to  be  distinctly 
below  the  standard  strength. 
The  necessity  of  being  very  accurate,  compelled  me  to  make  re- 
peated experiments  ;  and  anxious  for  a  variety  of  samples  I  applied 
to  several  chemists  in  the  neighborhood,  who  very  kindly  acceded  to 
my  requests,  and  gave  me  the  opportunity  of  more  extended  ex- 
perience. 
The  results  I  am  thus  able  to  show  will  perhaps  be  interesting  to 
the  association,  although  I  am  well  aware  that  this  subject  has  fre- 
quently been  treated  by  more  competent  observers.  I  may  especially 
call  to  your  recollection  a  communication  by  Dr.  Tilden,  published  in 
the  Pharmaceutical  Journal  of  July  29th,  1871  ;  also  a  paper  read 
by  Mr.  Abraham  before  the  Liverpool  Chemists'  Association  on  the 
8th  of  May,  1873;  and  likewise  Mr.' Siebold's  report  on  the  "Purity 
of  Commercial  Specimens  of  Officinal  Acids,"  which  will  be  found 
amongst  the  transactions  of  the  last  meeting  of  the  Pharmaceutical 
Conference  ;  and  I  trust  these  gentlemen  will  forgive  my  saying  that 
my  results  tend  to  corroborate  theirs. 
It  is  not  necessary  to  say  one  word  here  concerning  the  preparation 
of  hydrocyanic  acid  ;  indeed,  the  exact  process  does  not  seem  to  be  of 
much  importance,  provided  the  solution  contains  2  per  cent,  of  real 
acid. 
The  Pharmacopoeia  gives  two  tests  for  estimating  its  strength.  The 
cyanogen  may  either  be  precipitated  and  weighed  as  dry  cyanide  of 
silver  or  tested  volumetrically  with  a  standard  solution  of  nitrate  of 
silver.  This  latter  was  the  method  we  preferred  to  adopt,  and,  in 
practice,  found  it  convenient  to  employ  a  nitrate  of  silver  solution  of 
such  strength  that  40  c.c.  would  show  1  per  cent,  in  4  grammes  of 
sample."  (I  say  we,  because  throughout  these  experiments  I  was 
kindly  assisted  by  Mr.  Schacht.) 
Briefly  then,  we  dissolved  3-15  grams  of  dried  nitrate  of  silver 
*  Read  at  a  meeting  of  the  Bristol  Pharmaceutical  Association,  December 
12,  1873. 
