Am.  jour.  Pharm.  if  Examination  of  Commercial  Dextrin.  ci 
January,  19 19.    J  J  0A 
as  starch  the  carbohydrate  or  group  of  carbohydrates  which, 
whether  soluble  in  cold  water  or  not,  form  a  solution  or  gelatinize 
with  hot  water,  give  a  blue  color  on  treatment  with  iodine,  and  are 
precipitated  by  semi-saturation  of  the  cold  solution  with  barium 
hydroxide. 
By  dextrin  gum  is  meant  the  mixture  which  results  from  the 
hydrolysis  of  starch  when  the  change  has  not  been  carried  so  far 
as  a  complete  conversion  into  sugars,  thought  the  latter  may  be 
present  in  the  gum.  "  Dextrin  gum  "  gives  no  blue  color  with  iodine 
and  is  soluble  both  in  cold  water  and  in  a  cold,  half-saturated  solu- 
tion of  barium  hydroxide. 
The  method  of  Lamb  and  Harvey2  for  the  analysis  of  these 
mixtures  is  not  satisfactory.  It  includes  as  "  starch "  only  insol- 
uble starch,  while  soluble  starch  is  determined  as  part  of  the  "  dex- 
trin." We  have  found  that  when  the  starch  and  dextrin  are  mixed 
in  certain  proportions  it  is  very  difficult  to  wash  the  former  free 
from  the  latter  with  water;  filtration  is  very  slow  and  the  starch 
passes  into  solution  during  the  process  to  a  serious  extent.  With 
reference  to  our  first  objection,  we  admit  that  for  many  commercial 
purposes  it  may  be  desirable  to  determine  soluble  starch  among  the 
dextrins.  To  adopt  such  a  practice  in  our  own  laboratory,  however, 
would  not  be  satisfactory,  as  importers  would  thereby  be  penalized. 
A  method  of  examination  which  is  both  short  enough  for  prac- 
tical purposes  and  scientifically  accurate  is  much  to  be  desired,  but 
for  the  present  we  have  aimed  at  simplicity  of  procedure  and  a  prob- 
able error  of  less  than  5  per  cent. 
Determination  of  Dextrin  Gum. — The  sample  (1  Gm.)  is  warmed 
in  a  100  Cc.  graduated  flask,  with  30  Cc.  of  water  until  just  gela- 
tinized, and  cooled  quickly ;  50  Cc.  of  a  cold  saturated  barium 
hydroxide  solution  is  next  added  (the  flask  being  meanwhile  shaken), 
followed  by  enough  water  to  bring  the  total  volume  to  100  Cc.  The 
solution  is  filtered  through  a  dry  15  Cm.  paper  and  an  aliquot  por- 
tion (50  Cc.)  of  the  filtrate  is  pipetted  into  a  platinum  dish.  After 
the  addition  of  2  drops  of  a  1  per  cent,  phenolphthalein  solution, 
N/i  hydrochloric  acid  is  added  cautiously  till  the  neutral  point  is 
just  passed.  A  faint  pink  color  is  then  restored  by  the  addition  of 
two  or  three  drops  of  the  barium  hydroxide  solution.  A  weighed 
quantity  (about  10  Gm.)  of  sand  is  added,  and  the  dish  heated  on 
a  water-bath.    The  sand  should  be  stirred  when  almost  dry,  to  ex- 
2  J.  Soc.  Dyers  and  Col,  1918,  34,  10;  this  Journal,  1918,  133. 
