346       EMPLOYMENT  OF  MEDICINAL  HYDROCYANIC  ACID. 
strength.  This  is  certainly  an  unsatisfactory  and  unsafe  state 
of  things. 
In  the  first  place,  I  think  I  am  warranted  in  affirming  that  the 
illustrious  Swedish  chemist  never  promulgated  any  formula  for 
the  preparation  of  a  medicinal  hydrocyanic  acid.  I  have  care- 
fully searched  his  essays,  and  his  letters  to  Crell,  as  well  as  his 
treatise  on  Air  and  Fire,"  and  could  find  nothing  but  an  ac- 
count of  prussic  acid,  with  "which  he  conducted  certain  chemical 
researches  with  a  view  of  ascertaining  its  nature  and  efi*ects  on 
other  substances,  but  not  having  the  least  reference  to  its  em- 
ployment as  a  medicine ;  nor  were  any  medical  effects  at  that 
time  attributed  to  it.  The  acid  he  used  was  prepared  from  com- 
mercial Prussian  blue,  a  substance  of  variable  composition,  as  he 
himself  ascertained.  A  mixture  of  commercial  Prussian  blue, 
red  precipitate,  and  water  was  boiled ;  the  filtered  solution  was 
presented  to  the  action  of  iron  filings  and  dilute  sulphuric  acid, 
the  clear  liquid  thus  produced,  being  decanted,  was  distilled, 
and  one-fourth  drawn  off ;  a  few  grains  of  chalk  were  added, 
and  the  liquor  was  re-distilled  into  a  receiver  containing  "  a 
little  water."  The  whole  of  what  Scheele  wrote  on  the  subject 
is  contained  in  his  21st  essay. 
Here  we  do  not  discover  any  care  to  produce  hydrocyanic 
acid  of  such  normal  strength  as  would  insure  identity  of  power 
in  - the  same  dose,  at  all  times,  with  different  samples  of  the 
medicine.  I  conclude,  therefore,  that  the  name  "  Scheele's 
acid  "  is  a  misnomer,  leading  to  misconception,  and  even  to 
danger. 
No  doubt  a  formula  for  hydrocyanic  acid  was  introduced  into 
the  Pharmacopoeia  of  the  United  States  (1820)  under  the  name 
of  Scheele's  acid,  prepared  from  the  same  materials  as  those 
used  by  Scheele,  but  in  different  proportions,  by  a  different 
method,  and  with  a  different  result.  This  I  believe  to  be  the 
origin  of  the  name  "  Scheele's  prussic  acid."  But,  as  observed 
by  Jourdan,  la  densite  variable  de  I'acide  hydrocyanique  pre- 
pare suivant  la  methode  de  Scheele  ne  permet  pas  de  I'appliquer 
aux  usages  de  la  medecine." 
The  acid  prepared  according  to  ,the  British  Pharmacopoeia, 
as  that  authority  informs  us,  contains,  by  weight  of  the  solution. 
