28 
Sterculia  Gum. 
Am.  Jour.  Pharm . 
Jan.,  1890. 
EXPLANATORY  NOTES  ON  SOME  OF  THE  RESULTS  RECORDED  IN 
THE  FOREGOING  TABLES. 
No.  14.  "  Some  tragacanth  was  digested  with  fifty  times  its  weight 
of  water  containing  1  per  cent,  of  hydrochloric  acid  in  a  water-bath 
until  dissolved ;  it  was  then  filtered  and  excess  of  baryta  water  added. 
The  precipitate,  which  formed  slowly,  was  pectate  of  baryta.  When 
of  a  suitable  consistence,  this  was  washed,  suspended  in  water  and 
treated  with  excess  of  hydrochloric  or  acetic  acid,  which  left  a  precipi- 
tate of  pure  pectic  acid.  As  the  result  of  numerous  determinations, 
it  was  found  that  by  this  method  about  60  per  cent,  of  pectic  acid  can 
be  obtained  from  gum  tragacanth  "  (Pharm.  Journ.  [3],  v,  766  ;  vii, 
773).  On  repeating  these  experiments  with  tragacanth  the  results 
were  as  indicated  by  Giraud.  After  some  little  time  there  was  formed, 
on  addition  of  baryta  water  in  excess,  a  whitish  or  opalescent  precipi- 
tate of  pectate  of  baryta,  very  similar  in  appearance  to  weak 
mucilage  of  tragacanth.  The  precipitation  was  complete  in  forty- 
eight  hours.  Sterculia  gum  substituted  for  tragacanth  gave  negative 
results. 
No.  11.  Addition  of  alcohol  to  dilute  acidulous  solution. 
Sterculia. — The  liquid  becomes  cloudy  throughout  its  whole  bulk, 
behaving  in  much  the  same  way  that  a  weak  solution  of  arabin  would 
if  similarly  treated.    It  is,  in  fact,  found  to  be  arabin. 
Tragacanth. — A  glairy  substance  is  formed,  the  transparency  of  the 
liquid  being  scarcely  impaired.  On  standing  this  jelly-like  body  rises 
to  the  top  of  the  liquid.    This  is  pectin,  according  to  Giraud. 
Table  Showing  the  Average  Composition  of  Sterculia  Gum. 
Eupestris. 
Diversifolia. 
Urens. 
Soluble  in  cold  water  (chiefly  arabin).. 
6-9 
63-42 
20-52 
9015 
9-88 
61-74 
20  2 
8-195 
3-14 
75'1 
16-6 
5-83 
99-855 
100-015 
100-67 
The  author's  discovery  of  pararabin  in  Sterculia  gum  really  con- 
firms Fliickiger's  figures  obtained  by  combustion  of  the  gum  of  S. 
Tragacantha  (Pharm.  Journ.  [2],  x,  642).  His  percentage  results  are 
practically  identical  with  the  generally  accepted  figures  for  arabin, 
