^Au^uYtiissT*}         Estimation  of  Hydrocyanic  Acid.  409 
mountable,  and  that  it  is  of  importance  to  complete  and  render  more 
precise  the  study  of  the  ptomaines. 
Note. — Those  interested  in  the  study  of  the  putrefaction  alkaloids 
will  find  two  valuable  contributions  relating  to  their  [formation  and 
chemical  composition  in  the  '^Berichte  der  Deutsch.  Chem.  Ges./'  1883, 
pp.  1186-1195,  entitled  "Zur  Kenntniss  der  Faulnissalkaloi'de'^  (a  con- 
tribution to  the  knowledge  of  the  putrefaction  alkaloids),  by  L.  Brieger, 
and  "Ueber  basische  Faulnissprodukte^' [^(on  basic  putrefaction  prod- 
ucts), by  E.  and  H.  Salkowski.— F.  B.  P. 
THE  UNITED  STATES  PHARMACOPCEIA  PROCESS  FOR 
THE  ESTIMATION  OF  HYDROCYANIC  ACID.^ 
By  K.  a.  Cripps. 
Assistant  in  the  Laboratories,  Bloomsbury  Square. 
The  directions  given  in  the  United  States  Pharmacopoeia  for  the 
estimation  of  hydrocyanic  acid  are  as  follows :  13*5  grams  of  dilated 
hydrocyanic  acid,  diluted  with  30  cc.  of  water,  and  mixed  with  enough 
aqueous  suspension  of  magnesia  to  make  the  mixture  quite  opaque,  and 
afterwards  with  a  few  drops  of  solution  of  chromate  of  potassium,, 
should  require  50  cc.  of  the  volumetric  solution  of  nitrate  of  silver^ 
before  the  red  color,  caused  by  the  latter  ceases  to  disappear  on  stirring 
(corresponding  to  the  presence  of  2  per  cent,  of  absolute  hydrocyanic 
acid)."  On  reading  this  I  was  struck  by  the  small  amount  of  solution 
of  nitrate  of  silver  required,  and  on  calculating  the  amount  theoretically 
required  to  precipitate  the  whole  of  the  hydrocyanic  acid  as  cyanide  of 
silver  found  it  to  be  100  cc.  instead  of  50  cc.  Assuming  the  forma- 
tion of  a  double  salt  of  cyanide  of  silver  and  cyanide  of  magnesium  of 
the  formula  MgCy2(AgCy)2,  and  assuming  also  that  chromate  of  silver 
will  be  precipitated  as  soon  as  the  double  salt  is  completely  formed,, 
then  the  figures  given  in  the  U.  S.  Pharmacopoeia  would  be  correct. 
The  object  of  the  experiments  shortly  detailed  in  this  note  was  to- 
prove,  first,  whether  or  no  the  U.  S.  Pharmacopoeia  is  correct  in  assuming 
that  chromate  of  potassium  will  indicate  the  complete  formation  of 
double  cyanide  of  magnesium  and  silver  (if  such  exist),  in  the  estima- 
tion of  hydrocyanic  acid,  or  whether  it  will  only  indicate  the  precipita- 
tion of  the  whole  of  the  cyanogen  as  cyanide  of  silver;  and  second. 
^  Read  before  the  School  of  Pharmacy  Students'  Association. 
