Amsipt!;l89hoarm"}  Assay  of  Gum  Arabic  and  G.  Senegal.  461 
form  of  M.  Azedarach,  Linn.,  may  be  instanced  together  with  the 
spotted  or  leopard-tree  gum  (Flindersia  maculosa).  These  are  the 
only  other  exudations  of  the  Meliacece  recorded  as  far  as  I  know.  I 
have  seen  and  examined  them  and  they  are  true  gums. 
ASSAY  OF  GUM  ARABIC  AND  GUM  SENEGAL.1 
By  Liebermann. 
(1)  Gum  arabic  forms  round  or  angular,  colorless,  yellowish  or 
brownish  lumps,  which  strongly  refract  the  light,  and  look  as  if 
they  possessed  a  crystalline  structure.  Owing  to  the  disturbed  state 
of  trade  in  the  Soudan,  much  of  the  gum  arabic  nowadays  imported 
is  partly,  or  even  totally,  composed  of  gum  Senegal. 
(2)  Gum  Senegal  forms  either  colorless  or  yellowish  lumps,  some- 
what whitish  on  the  surface  (resembling  corroded  glass),  the  interior 
of  which  is,  however,  clear  and  lustrous.  The  lumps  are  generally 
longish,  straight  or  bent,  vermicular  or  cylindric.  Sometimes  they 
look  as  if  small  lumps  have  deposited  round  a  larger  one.  They 
have  to  a  certain  extent  the  shape  of  mulberries.  If,  therefore,  the 
sample  is  not  in  powder  or  too  small  lumps  the  very  appearance  will 
tell  the  fraud. 
(3)  Both  varieties  are  completely  soluble  in  water ;  there  only 
remains  .small  particles  of  wood,  which,  in  samples  of  gum  arabic, 
are  generally  reddish,  but  blackish  in  the  gum  Senegal.  These 
woody  particles  are  found  even  in  the  superior  kinds  of  the  gum. 
Other  gums,  like  cherry  gum,  are  only  partly  soluble  in  water. 
There  remains  a  jelly  which  only  dissolves  on  prolonged  boiling. 
(4)  The  watery  solution  of  both  gums  gives  with  potash-lye  and 
a  few  drops  of  solution  of  copper  sulphate  bluish  precipitates  ;  but 
with  gum  arabic  the  precipitate  is  more  abundant,  sticks  together, 
and  rises  to  the  surface  of  the  fluid.  The  precipitates  are  not  dis- 
solved on  heating  and  do  not  reduce  the  copper. 
(5)  Dextrin  solution  also  gives  a  blue  precipitate,  but  this  dis- 
solves completely  on  warming  to  a  clear  dark-blue  fluid.  On  pro- 
longed boiling  the  copper  gets  completely  reduced. 
(6)  Heated  for  a  long  time  with  dilute  potash,  gum  arabic  or 
dextrin  turn  amber-yellow,  whilst  gum  Senegal  scarcely  colors 
at  all. 
1  Client.  Zeit.,  No.  41,  1890.    Reprinted  from  The  Analyst,  August,  1890. 
