ON  THE  COPAL  OF  ZANZIBAR. 
441 
Thus  the  percentage-amounts  are  for      I.  II. 
Carbon  ....  41-98  41-76 
Hydrogen  ....       5-59  5-91 
The  formula  of  gum  arable  shows  the  following  numbers  : 
12  G       .       144       .  42-12 
22  H      .        22       .  6-41 
11  0       .       176       .  51.47 
324  100-00 
other'^similar  gums,  however,  are  usually  re- 
144      .  44-44 
20       .  6-17 
160       .  49-39 
324  100-00 
I  restrict  myself  for  the  moment  to  the  mere  communication 
of  the  above  facts  and  will  not  enter  into  the  discussion,  whether 
a  gum,  tragacanth  or  bassorin,  exists  or  not,  to  which  the  formula 
CigHjoOjo  should  be  assigned.  Perhaps  all  the  various  kinds  of 
these  bodies  may  be  referred  to  one  and  the  same  formula.  The 
African  tragacanth  at  least  corresponds  rather  in  this  respect 
with  gum  arable. 
From  the  experiments  here  detailed  I  infer,  that  the  African 
Sterculia-tragacanth  may  be  used  both  in  pharmacy  and  in  the 
arts  instead  of  the  usual  drug  of  Asia  Minor.  When  the  Niger 
and  its  tributaries  are  opened  to  trade,  this  gum  may  possibly 
form  an  important  item  of  exportation.^ — Pharm.  Journ.,  ^f^y^ 
1869. 
ON  THE  COPAL  OF  ZANZIBAR. 
Extract  from  a  letter  from  John  Kirk,  M.D..  F.L.S.,  dated  Zanzibar, 
March  20,  1868. 
The  vegetation  along  the  creek  of  Dan  Salam*  consists  of 
many  curious  and,  to  me,  unknown  bushes,  with  heavy  timber 
scattered  here  and  there ;  among  them  was  the  Trachylohium 
Mossamhicense,  Kl.,  distinguished  by  its  rounded  head  of  glossy 
[*  Dan  Salam  is  stated  in  the  letter  to  be  a  spacious  creek  opposite  the 
southern  end  of  Zanzibar  Island. — Ed.] 
Common  tragacanth  and 
ferred  to  the  formula 
12  C 
20  H 
10  0 
