EMPLOYMENT  OF  MEDICINAL  HYDROCYANIC  ACID.  347 
2  per  cent,  of  hydrocyanic  acid  ;  100  grains  of  it  precipitated 
with  a  solution  of  nitrate  of  silver  yield  10  grains  of  dry  cyanide 
of  silver.  The  unauthorised  hydrocyanic  acid  prepared  in  Lon- 
don as  Scheele's  strength  "  contains  5  per  cent,  of  real  acid  ; 
100  grains  of  it  by  weight  should  produce  25  grains  of  dry 
cyanide  of  silver  when  precipitated  by  solution  of  nitrate  of 
silver.  Thus,  if  five  minims  were  intended  as  a  dose  for  the  for- 
mer, the  patient  would  practically  have  taken  twelve  minims  if 
Scheele's  strength  were  made  use  of.  What  the  effect  of  such  a 
dose  might  be,  if  repeated  at  intervals  during  the  day,  it  is  not 
for  me  to  inquire.  Of  hydrocyanic  acid,  B.  P.,  at  the  tempera- 
ture of  60°,  one  drachm  measure  is  equal  to  about  71  drops  of 
the  same  acid  dropped  from  an  ordinary  ounce  bottle  ;  hence, 
12  minims  would  be  equal  to  14|  drops. 
Some  make  light  of  a  dose  of  three  or  four  drops  because  they 
have  known  larger  doses,  to  prove  harmless  ;  but  were  they  quite 
sure  of  the  condition  of  the  acid  employed  ?  It  is  to  be  kept  in 
mind  that  concentrated  hydrocyanic  acid  rapidly  deteriorates, 
that  even  the  dilute  acid  of  the  Pharmacopoeia  becomes  weaker 
by  age,  and  that  the  so-called  Scheele's  acid,  being  stronger 
than  the  latter,  is  still  more  liable  to  change  ;  hence,  from  its 
very  weakness,  arises  another  source  of  danger.  On  this  subject 
Professor  W.  Gregory  has  thus  expressed  himself:  "  The  aver- 
age dose  (of  the  medical  acid)  safe  for  an  adult  is  one  or  two 
drops.  It  is  much  used  as  a  sedative  and  anodyne  ;  but,  unless 
its  strength  and  dose  be  perfectly  known,  it  is  a  dangerous 
remedy.  Fatal  accidents  have  occurred  from  prescriptions  found, 
after  experience,  to  act  favorably,  being  made  up  in  another 
place,  or  by  the  same  druggsit  with  a  fresh  stock,  this  fresh 
stock  being  exactly  of  the  standard  strength,  while  the  previous 
acid  had  lost  so  much  by  keeping  that  the  dose  had  been  of 
necessity  increased.  There,  danger  actually  arose  from  a  too 
weak  acid  having  been  used."  ("Organic  Chemisty,"  4th 
edition,  p.  75.) 
In  all  cases  it  will  occasionally  be  necessary  to  test  the  con- 
dition of  the  hydrocyanic  acid  employed  by  the  volumetric 
method  directed  in  the  B.  P.  And  it  would  still  further  con- 
duce to  the  safe  employment  of  this  dangerous  medicine  if,  in^ 
