Am.  Jour.  Pbarm.  ) 
August,  1884.  j 
Ferric  Chlorides, 
409 
remains.  In  order  to  dry  this  perfectly  a  moderately  high  and  pro- 
longed heat  is  necessary.  It  then  becomes  pulverulent  and  unhygro- 
scopic.  Even  in  this  condition,  it  long  after  slowly  dissipates  nitrous 
vapors.  On  mixing  a  little  alcohol  with  the  pasty  residue  and  placing 
it  in  a  warm  locality  it  dries  up  to  a  light  friable  mass  utterly  free 
from  nitrous  compounds  and  deliquescent  tendency.  These  results 
show  that  the  usual  methods  do  not  prevail  against  the  presence  of 
nitric  acid  and  the  lower  oxides  of  nitrogen.  They,  however,  adduce 
powerful  evidence  that  alcohol  is  the  effective  purifying  agent,  and  that 
after  its  influence  has  been  exerted  upon  the  usual  forms  of  ferric  salts, 
developed  by  nitric  acid,  they  cease  to  generate  nitrous  ether  in  the 
presence  of  alcohol.  Under  ordinary  conditions  nitric  acid  does  not 
directly  react  upon  alcohol  and  form  ethyl  nitrate,  it  is  first  reduced, 
in  decomposing  a  part  of  the  alcohol,  to  nitrous  acid  which  then  com- 
bines with  the  remaining  alcohol  and  produces  ethyl  nitrite.  When 
nitrous  oxide,  that  is,  nitrogen  trioxide,  comes  in  contact  with  alcohol, 
it  also  gives  rise  to  ethyl  nitrite.  Nitrogen  tetroxide  in  reacting  upon 
bases  effects  the  formation  of  a  mixture  of  nitrates  and  nitrites  and 
hence  when  alcohol  slowly  absorbs  this  gas,  nitric  acid  and  ethyl  nitrite 
result.  Nitrogen  dioxide  does  not  exert  a  direct  effect  itself,  but  its 
oxidation  producing  the  tetroxide  consequently  leads  to  an  identical 
product.  From  this  it  is  seen  that  the  chief  factors  in  the  develop- 
ment of  an  ether  in  tincture  of  ferric  chloride  are  three  lower  oxides  of 
nitrogen,  namely,  the  di,  tri,  and  tetroxide,  whilst  nitric  acid  acts  but 
indirectly,  and  chlorhydric  acid  is  wholly  inert.  In  the  "American 
Journal  of  Pharmacy"  of  April,  1876,  p.  177,  the  writer  has  already 
dwelt  upon  similar  considerations.  If  the  Pharmacopoeia  insists  on 
the  method  of  transformation  by  means  of  nitric  acid  with  a  view  to 
the  exceptional  purity  of  the  product,  it  is  certainly  not  attaining  its 
object.  To  secure  this  end  it  must  either  purify  the  crude  product  by 
means  of  alcohol  or  abandon  the  nitric  acid  process.  If,  then,  after 
producing,  by  whatever  means,  a  compound  of  the  desired  quality,  the 
ether-forming  feature  will  naturally  disappear.  However,  if  this 
adjunct  is  deemed  essential,  it  can  readily  be  supplied  by  the  addition 
of  about  4  per  cent,  of  spirit  of  nitrous  ether.  This  procedure  would 
also  impart  a  more  definite  and  practical  character  to  the  preparation. 
In  regard  to  the  official  proportion  of  alcohol  in  the  tincture,  it  may 
be  said  that  it  is  unnecessarily  great.    Whilst  a  moderate  amount,  say 
