Am'sep^'i?8h6frm"}       Salicylic  Acid  and  Monad  Salts.  421 
cylate  causes  the  precipitation  of  crystalline  salicylic  acid  in  profusion. 
It  is  therefore  apparently  remarkable  that  a  normal  acetate  as  abund- 
antly dissolves  free  salicylic  acid.  It  seems  furthermore  doubly 
strange  that  one  molecule  of  the  acetate  conditions  the  solution  of  one 
molecule  of  the  acid.  This  solution  is  however  but  temporary  as  it 
gradually  deposits  a  considerable  proportion  of  free  acid.  When  this 
liberated  acid  is  reconverted  into  potassium  salt  and  reunited  with  the 
remaining  solution  no  subsequent  separation  occurs,  not  even  in  the 
presence  of  any  amount  of  excess  of  acetic  acid.  This  result  shows 
that  a  certain  proportion  of  potassium  acetate  is  essential  to  keep  all 
the  salicylic  acid  in  solution  in  the  presence  of  acetic  acid  largely  in 
excess.  It  was  found  that  this  is  effected  when  three  molecules  of  the 
acetate  react  upon  two  molecules  of  salicylic  acid,  that  is,  in  the  propor- 
tion of  294  parts  of  the  first  and  276  parts  of  the  second.  Since  the 
commercial  potassium  acetate  is  always  more  or  less  damp  and  indefi- 
nite, it  is  better  to  employ  instead,  300  parts  of  perfectly  dry  and  well 
crystallized  potassium  bicarbonate  neutralized  with  acetic  acid  aided  by 
warmth.     The  expression  for  the  reaction  is  written 
3(K  Ac) + 2(HS1 ) =2(KS1) + K  Ac(HAc)2. 
This  makes  it  apparent  that  only  enough  acetic  acid  is  displaced 
to  generate  one  molecule  of  acid  potassium  acetate  which  then  protects 
two  molecules  of  the  salicylate  in  the  presence  of  more  acetic  acid. 
This  solution,  when  moderately  dilute,  has  a  not  unpleasant  acidulous 
taste  and  hence  widely  different  from  the  nauseous  flavor  of  unmixed 
salicylate. 
Pure  potassium  salicylate,  when  crystallized  on  a  slide  and  viewed 
under  the  microscope,  is  seen  to  be  in  the  form  of  stellate  groups  having 
a  fine  appearance  in  polarized  light.  When,  however,  crystallized  in 
a  similar  manner  from  the  acetate  solution  it  is  presented  in  a  greatly 
improved  shape,  being  especially  elegant  under  the  polariscope.  It  is 
best  seen  with  a  half  inch  objective.  The  rays  constituting  the  star 
crystal  emanate  from  a  common  center  without  intercrossing.  The 
rays  thicken  towards  their  middle  and  then  again  attenuate.  They 
have  a  rather  irregular  contour  and  in  the  finest  samples  appear 
slightly  curved. 
POTASSIUM  CITEATE. 
Salicylic  acid  is  abundantly  dissolved  by  potassium  citrate.  The 
somewhat  dilute  solution  has  an  acidulous  hot  disagreeable  taste. 
