Am.  Jour.  Pharm. 
May,  1876. 
A  Singular  Reaction. 
213 
presence  of  iron  in  minute  quantity  was  suspected  in  the  syrup  of 
squill  and  spirit  of  nitrous  ether  ;  and,  on  applying  the  tests  for  this 
metal  to  the  two  preparations,  as  obtained  from  various  sources,  dis- 
tinct evidences  of  a  minute  quantity  of  iron  were  obtained. 
In  order  to  show  with  what  ease  this  contamination  (it  can  hardly  be 
called  an  adulteration)  creeps  into  the  preparation  of  spirit  of  nitrous 
ether,  a  small  quantity  was  placed  in  a  glass  vessel  and  stirred  for  a 
few  moments  with  an  iron  spatula,  when  a  drop  or  two  of  solution  of 
ferrocyanide  of  potassium  was  added — a  characteristic  blue  precipitate 
resulted.  The  explanation  is  simple,  sufficient  acid  being  usually  pres- 
ent in  spirit  of  nitrous  ether  to  act  upon  the  metal  and  form  a  soluble 
salt.  When  a  partly-worn  tinned  iron  measure  is  used  by  the  manu- 
facturer or  wholesale  dealer  in  measuring  this  preparation  (as  is  often 
the  case),  a  trace  of  this  metal  would  surely  be  left  in  it,  particularly  if 
the  liquid  was  allowed  to  stand  in  the  measure  any  time.  Commercial 
acetic  acid,  and  even  some  of  the  finer  grades,  were  found  to  contain 
slight  traces  of  iron  ;  and  hence,  in  syrup  of  squill,  we  have  the  metal 
present  in  minute  quantity. 
Now,  why  does  the  green  coloration  appear  ?  Wild-cherry  bark 
contains  tannic  and  gallic  acid,  and  these  give,  with  small  quantities  of 
an  iron  salt,  a  dark-green  coloration  in  the  presence  of  an  acid  like 
acetic. 
In  order  to  show  that  the  tannic  and  gallic  acids  were  concerned  in 
producing  the  color,  an  infusion  of  wild-cherry  was  prepared  carefully, 
by  the  U.  S.  P.  formula,  to  which  was  added  spirit  of  nitrous  ether 
and  syrup  of  squill  in  the  same  proportion  as  in  the  prescription.  The 
same  play  of  colors  took  place  ;  first,  a  deepening  of  the  red,  then 
gradually  changing,  until  the  dark-green  appeared.  The  subsequent 
addition  of  a  trace  of  iron  still  further  deepened  the  coloration. 
Part  of  the  same  infusion  was  deprived  of  tannic  acid  by  shaking  it 
with  hydrated  sesquioxide  of  iron,  until  a  small  portion  of  the  filtrate 
failed  to  give  a  coloration  with  a  weak  solution  of  an  iron  salt.  When 
to  this  infusion  the  same  proportion  of  spirit  of  nitrous  ether  and  syrup 
of  squill  was  added,  as  in  the  prescription,  no  change  in  color  was  ob- 
served, even  after  standing. 
The  presence  of  a  slight  excess  of  acid  favors  the  formation  of  the 
green  coloration  ;  and  when  an  alkaline  solution  is  added,  the  green 
coloration  disappears,  and  a  slight  precipitation  takes  place. 
