152 
REMARKS  OF  POLYGALIC  ACID. 
This  substance  is  soluble  in  water,  when  heated ;  less  soluble 
in  alcohol ;  gritty  between  the  teeth  ;  has  no  taste  of  senega  ; 
fuses  by  heat,  blackens,  and  is  almost  entirely  consumed. 
Concentrated  SO3  dissolves  it  with  heat  without  the  evolution 
of  either  ammonia  or  HC1.  Its  aqueous  solution  is  not  pre- 
cipitated by  either  chloride  of  barium  or  nitrate  of  silver.  A 
crystal  placed  on  moistened  litmus  paper  produced  a  reddish 
spot.  It  is  possible  that  this  substance  is  an  acid  salt  of  malic 
or  some  analogous  acid.  The  small  quantity  of  ash  it  leaves  is 
alkaline.    The  investigation  was  not  pushed  further. 
The  liquid,  from  which  the  crystals  deposited,  by  evaporation 
yielded  an  extract  tasting  strongly  of  senega. 
As  regards  the  pharmaceutical  applications  of  polygalic  acid, 
several  experiments  were  made  : — 
1.  Five  grains  of  the  acid  in  a  fluid  ounce  of  water,  kept  in 
a  vial  for  two  months,  acquired  a  foetid  odor,  whilst  a  portion  of 
matter  precipitated,  yet  the  taste  of  the  solution  was  strongly 
that  of  senega. 
2.  Five  grains  of  the  acid  were  dissolved  in  an  ounce  of 
cold  water,  with  five  grains  of  bi-carbonate  of  potassa,  and  kept 
the  same  length  of  time.  This  solution  also  spoiled,  but  re- 
tained its  senega  taste. 
The  best  form  of  prescribing  polygalic  acid,  in  liquid  form,  is 
with  syrup  of  gum  arabic,  to  blunt  its  acrimony.  It  is  necessary 
to  dissolve  it  in  a  little  hot  water,  and  add  it  warm  to  the  syrup 
of  gum,  and  mix  them.  It  may  also  be  added  to  syrup  of  ipe- 
cacuanha to  increase  its  expectorant  power.  But  the  form  best 
adapted  to  administer  this  principle  is  in  pills  and  powders.  In 
doses  of  one  or  two  grains  (which  represent  15  to  30  grains  of 
senega)  the  full  effect  of  a  table  spoonful  and  a  fluid  ounce  of 
decoction  of  senega  is  obtained.  Where  a  more  gentle  effect  is 
desired,  the  dose  must  of  course  be  greatly  reduced,  to  \  or  \ 
of  a  grain,  and  can  be  associated  with  ipecac,  tartar  emetic,  and 
other  medicine  with  which  senega  is  given.  When  the  form  of 
powders  is  adopted,  a  mixture  of  powdered  gum  and  sugar  should 
always  be  added  to  blunt  the  acrimony  of  the  polygalic  acid. 
Sugar  of  milk  triturated  with  the  acid,  in  the  proportion  of  1 
grain  to  9  grains,  is  an  eligible  form  for  use. 
In  cough  mixtures,  when  not  contra-indicated  or  incompati- 
