198  Observations  on  Acacia  of  Commerce.     { ^'ISxiiJm^' 
traces  of  dextrin  and  starch  were  added  to  the  sample  under  exam- 
ination ;  the  reagent  in  all  cases  gave  prompt  indication  of  their 
presence,  showing  that  there  was  present  in  the  original  sample 
nothing  to  mask  the  reaction. 
The  potassium  ferricyanide  reaction  did  not  give  satisfactory 
results.  The  test  solution  was  prepared  as  above  described  from 
clear  crystals  of  potassium  ferricyanide,  previously  washed  with 
distilled  water  to  free  it  from  any  adherent  ferrous  salt,  which  might 
have  formed  by  exposure  to  light.  By  reduction  with  the  ferric 
chloride  it  produced  a  pure  yellowish  brown  color,  without  a  bluish 
shade,  proving  the  absence  of  ferrous  salt. 
(a)  When  diluted  with  distilled  water,  it  remained  unchanged 
during  twelve  hours. 
{b)  A  1  per  cent,  solution  of  dextrin  in  distilled  water  caused 
almost  immediate  reduction  and  consequently  a  blue  color. 
(c)  The  reaction  with  finely  powdered  gum  arabic  proved  some- 
what less  rapid  than  that  with  pure  dextrin,  but  the  blue  color  was 
produced  within  twenty  minutes  (powder  free  from  dextrin  by  iodine 
test). 
(d)  Powdered  gum  arabic,  adulterated  with  dextrin,  reduced  the 
solution  after  a  few  minutes'  time. 
(e)  When  a  tear  of  the  gum  was  dropped  into  the  solution  of 
potassium  ferricyanide,  the  solution  did  not  acquire  a  blue  color 
within  two  hours ;  but  after  standing  a  few  minutes  the  outer  sur- 
face of  the  tear  of  gum  was  colored  a  decidedly  bluish  tinge.  When 
a  tear  of  the  gum  was  powdered,  and  then  some  of  the  potassium 
ferricyanide  solution  added,  reduction  with  formation  of  a  blue  color 
took  place  more  rapidly,  agitation  increasing  the  action. 
Is  it  not  possible  that  the  drying  of  the  gum  or  that  other  influ- 
ences cause  a  change  to  take  place  in  the  gum  acacia,  which  might 
account  for  the  reaction  with  alkaline  cupric  tartrate  and  potassium 
ferricyanide  solutions  ? 
In  order  to  determine  the  quality  of  the  commercial  powdered 
acacia,  the  samples  were  obtained,  as  far  as  possible,  from  the  source 
of  supply  of  the  market,  though  the  majority  were  obtained  in  phar- 
macies in  Ohio,  Indiana,  New  York,  Pennsylvania  and  New  Jersey. 
All  the  samples  were  tasteless,  and  all  reduced  Fehling's  solution, 
as  described  in  the  first  part  of  this  contribution. 
