Am.  Jour.  Pharm. ) 
Dec  ,  1877.  f 
The  Acid  of  Willow  Bark. 
609 
THE  ACID  OF  WILLOW  BARK. 
By  D.  B.  Dott. 
The  chemistry  of  the  willow  seems  to  have  been  little  studied,  and 
what  attention  it  has  received  has  been  almost  entirely  devoted  to  its 
active  principle,  salicin.  All  the  information  I  have  been  able  to 
obtain  regarding  the  constituents  of  the  bark  is  very  meagre,  the 
majority  of  works  on  chemistry  and  materia  medica  merely  mentioning 
that  salicin  is  extracted  therefrom  ;  while,  curiously  enough,  the 
"  Pharmacographia,"  of  Fliickiger  and  Hanbury,  omits  all  notice  of 
the  subject.  Neligan  states  (authority  not  given)  that  the  baVk  contains 
resinous  matter,  gum,  chlorophyll,  tannin,  an  organic  salt  of  magnesia, 
and  salicin  ;  and  that  is  as  complete  an  account  as  I  have  found  in  any 
of  the  other  books. 
When  an  infusion  of  willow  bark  is  made  the  liquor  is  distinctly 
acid  to  litmus.  In  the  preparation  of  salicin  by  Erdmann's  process  this 
acid  is  neutralized  by  the  excess  of  lime,  and  the  salt  thereby  formed 
passes  into  solution.  On  evaporating  to  dryness  and  exhausting  the 
residue  with  spirit  the  salt  is  redissolved  and  remains  in  the  spirituous 
solution  after  the  salicin  has  crystallized  out.  The  salt  may  be  obtained 
by  distilling  off  the  spirit  and  allowing  the  residue  to  crystallize.  These 
crystals  are  then  purified  by  recrystallization  from  water.  Thus  prepared 
the  lime-salt  separates  in  the  form  of  a  cauliflower-like  mass,  composed 
of  radiate  groups  of  prismatic  crystals. 
A  portion  of  those  crystals  when  heated  fused,  and  inflamed,  left  a 
residue  of  calcic  carbonate,  indicating  an  organic  salt  of  lime.  It  was 
found  that  the  substance  lost  weight  but  slowly  in  the  exsiccator,  and 
likewise  in  the  water-bath.  A  portion  of  the  air-dried  salt  was  there- 
fore dried  in  the  air-bath  at  I30°C.  9-140  grs.  lost  2745  grs. =30*03 
per  cent.  In  another  determination  with  a  different  crop  of  crystals 
7*85  grs.  lost  2*275  grs. =28*98  per  cent.  A  quantity  of  the  salt  was 
then  incinerated  in  a  platinum  crucible,  the  residue  being  treated  with 
excess  of  sulphuric  acid  and  the  crucible  again  ignited.  6*41  grs.  gave 
4*00  grs.  CaS04=i*i76  grs.  Ca=i8*34  per  cent.  In  the  second 
determination  6*12  grs.  gave  3*82  grs.  CaSO=i*i2  grs.  Ca=i8*35 
per  cent. 
One  or  two  methods  for  preparing  the  acid  were  tried,  the  following 
being  the  process  finally  adopted :  To  a  solution  of  the  lime-salt  in 
water  solution  of  oxalic  acid  is  added — not  in  excess.    The  precipi- 
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