468  Mucilage  of  Gum  Arabic.  {%ltijm™' 
After  a  quarter  of  an  hour,  1  was  jelly-like ;  2,  somewhat  stiffer 
(bj  the  addition  of  one  drachm  of  water  it  could  be  shaken)  ;  3  could' 
be  freely  shaken  and  poured  out ;  4,  somewhat  between  2  and  3  ;  5,. 
just  the  same  ;  6,  stiff  jelly. 
After  twenty- four  hours,  1,  2,  4  and  5  were  quite  stiff;  addition* 
of  a  little  water  to  1  made  it  quite  fluid  ;  the  consistence  of  2,  4  and 
5  was  not  altered  ;  3  and  6  decidedly  hard. 
The  two  heavy  magnesia  mixtures  behaved  like  any  mixture  of 
water  and  an  insoluble  powder,  remaining  at  the  bottom  of  the  vialr 
but  very  easily  shaken  up. 
The  results  I  arrived  at  are  :  1st,  To  mix  light  calcined  magnesia 
with  not  less  than  twelve  parts  of  water  ;  or,  where  the  amount  of 
liquid  cannot  be  increased,  to  use  the  heavy  calcined  magnesia.  2dy 
Boiling  does  not  make  the  mixture  more  fluid.  3d,  Sugar  does  not 
prevent  hardening,  except  on  increasing  the  quantity  of  liquid,  and 
is  then  not  necessary. 
MUCILAGE  OF  GUM  ARABIC. 
The  instability  of  mucilage  of  gum  arabic,  when  prepared  in  accord- 
ance with  our  Pharmacopoeia,  makes  it  necessary  for  pharmacists  to* 
prepare  it  in  small  quantities  or  else  dispense  a  preparation  unfit  for 
medicinal  use.  In  fact,  during  the  summer  months,  the  mucilage- 
undergoes  change  so  soon  that  we  have  prepared  it  as  called  for,, 
using  granular  acacia.  This  has  been  a  serious  inconvenience,  and 
hoping  to  overcome  it,  we  made  a  few  experiments  last  May,  and 
found  that  by  substituting  "  tolu  water"  for  water,  the  mucilage 
kept  well  several  months. 
The  "  tolu  water  "  is  prepared  as  follows  : 
R.       Tinct.  Tolu  (saturated),  fgii. 
Carb.  Magnes.,       ......  %ir. 
Aquae,  Oii. 
Rub  the  tincture  first  with  the  carbonate  of  magnesium,  and  then 
with  the  water  gradually  added,  and  filter. 
The  mucilage  thus  prepared  has  a  faint  odor  and  flavor  of  tolu,. 
which  is  not  objectionable  and  in  many  instances  might  be  advan- 
tageous ;  in  appearance  it  is  identical  with  the  officinal. 
We  think  tolu  prevents  change  in  liquids  upon  the  same  principle 
and  just  as  effectually  as  benzoin  obviates  rancidity  in  unctuous  sub- 
