Am.  Jour.  Pharm. ) 
March,  1885,  j 
Tincture  of  Ferric  Chloride. 
115 
acid  or  even  nitrogen  oxides  formed  from  its  decomposition;  and  that 
the  excess  of  hydrochloric  acid  present  in  the  liquor  in  no  way  tends 
toward  the  etherization  of  the  alcohol  in  making  the  tincture,  and 
lastly,  that  this  result,  i.  e.,  the  etherizing  of  the  alcohol,  depends  upon 
the  presence  of  lower  oxides  of  nitrogen  arising  from  decomposed  nitric 
acid. 
In  regard  to  the  unremoved  excess  of  nitric  acid  in  the  liquor,  a  few 
remarks  confirming  the  statement  of  its  existence  there,  are  in  order. 
To  further  this  end,  the  following  plan  was  adopted  :  To  a  definite 
quantity  of  the  officinal  liquor,  silver  nitrate  was  added  to  precipitate 
all  chlorides;  care  being  used  to  avoid  any  excess  of  the  precipitant. 
The  filtered  liquid,  which  was  strongly  acid  in  its  reaction  with  litmus, 
readily  liberated  free  iodine  on  the  addition  of  a  very  small  quantity  of 
potassium  iodide.  To  ascertain  whether  this  acid  was  nitrous  or  nitric 
acid,  several  volumes  of  certain  diluted  acids,  equal  in  quantity  to  that 
of  the  liquor  originally  used,  were  each  taken  separately  and  exposed 
to  an  action,  if  possible,  upon  potassinm  iodide  in  the  same  amount  as 
that  used  above,  and  the  ensuing  reaction  or  non-reaction  used  as  a 
basis  of  comparison.  When  this  was  done,  diluted  hydrochloric  acid 
(U.  S.  P.,  1880)  had  no  decomposing  effect  upon  the  iodide,  neither 
had  diluted  nitric  acid,  so  that  when  the  so-called  pure  nitrous  acid  of 
commerce  (really  a  mixture  of  both  nitrous  and  nitric  acids),  very 
largely  diluted  with  water,  was  added  in  small  amounts  and  iodine 
freely  liberated,  the  evidence  given  clearly  showed  the  presence  in  the 
liquor  of  free  nitrous  acid  alone.  The  method  used  is  simply  a  modi- 
fication of  the  general  test  for  nitrites  in  the  presence  of  nitrates,  and 
depends  for  its  value  upon  the  fact  that  free  nitrous  acid  in  dilute  solu- 
tion quickly  decomposes  potassium  iodide  with  the  setting  free  of  its 
iodine,  while  free  nitric  acid,  under  like  conditions,  exerts  a  totally 
negative  influence. 
For  the  moment,  let  us  turn  our  attention  towards  certain  calcula- 
tions based  upon  the  officinal  formulte,  showing  the  amounts  of  the  two 
acids  ordered  and  that  actually  required.  Since  the  solution  contains 
37*8  parts  of  ferric  chloride  in  each  100  parts,  and  since  it  is  found 
that  324'2  parts  of  ferric  chloride  require  684*6  parts  of  31 '9  per  cent, 
hydrochloric  acid,  then  37*8  parts  of  ferric  chloride,  the  amount  ofli 
cinally  desired,  would  require  a  less  quantity.  It  is  so  expressed,  and 
80  parts,  in  short,  is  the  result  indicating  the  amount  actually  used 
