372  Chemical  Nature  of  Starch  Grains.        { j^'im^' 
groups,  i.  e.y  micellae,  which,  owing  to  their  comparatively  slow  move- 
ments, due  to  their  greater  size  and  weight,  easily  unite  into  micellar 
clusters,  the  author  concludes  that  swollen  starch  and  starch-paste 
differ  in  nothing  but  the  aggregate  condition  of  their  micellae ;  they 
differ  therefore  physically  but  not  chemically,  and  accordingly  starch- 
paste,  amidulin  and  granulose  are  identical. 
Erythrogranidose. — Erythrogranulose  and  erythrodextrin  are  the 
names  given  to  two  bodies  colored  red  by  iodine  (Briicke).  By  digest- 
ing starch  solution  with  diastase,  and  testing  portions  from  time  to 
time  with  iodine  and  with  tannin  solution,  it  was  shown  that  so  long 
as  iodine  produced  a  blue  coloration,  tannin  produced  a  precipitate,  but 
with  a  red  coloration  no  precipitate  was  formed,  nor  under  these  con- 
ditions was  a  precipitate  produced  by  adding  hydrochloric  acid ;  hence 
the  red  coloration  is  due  to  the  presence  of  dextrin.  If  very  dilute 
iodine  be  added  to  starch -granules  (or  paste)  a  red  color  is  first  pro- 
duced;, this  is  due  to  the  presence  of  dextrin  (erythrodextrin)  and  its 
greater  solubility  in  water. 
Amylodextrin. — W.  Nageli  states  that  soluble  starch  is  distinguished 
from  amylodextrin  by  being  precipitated  from  solution  by  tannin  and 
by  lead  acetate,  and  further  that  freshly  precipitated  starch  is  insoluble 
in  water,  whilst  freshly  precipitated  amylodextrin  is  soluble.  None  of 
these  differences  can  be  confirmed.  Further,  amylodextrin  does  not? 
like  starch,  swell  up  with  an  alkaline  solution,  but  simply  dissolves ; 
this,  however,  is  not  a  distinctive  test,  since  precipitated  starch  behaves 
exactly  like  amylodextrin  ;  amylodextrin  is  tinted  by  organic  matter 
just  as  starch  is.  It  is  also  stated  that  Trommer's  copper  test  is  not 
reduced  by  amidulin,  but  is  by  amylodextrin ;  but  it  has  been  shown 
that  the  starch-grains  themselves  contain  dextrin,  and  further,  during 
the  progress  of  the  test,  the  starch  becomes  converted  into  dextrin  and 
into  sugars,  and,  still  more  important,  dextrin  is  formed  during  the 
preparation  of  amylodextrin. 
The  author  has  been  quite  unable  to  confirm  the  statement  as  to  the 
crystalline  nature  of  amylodextrin.  Amidulin  and  amylodextrin  are 
identical.  That  amydulin — a  body  not  capable  of  diffusion,  can  be 
extracted  from  starch-grains  by  dilute  acid,  is  explained  by  the  action 
of  the  acid  on  the  micellar  aggregates. 
The  Iodine  Reaction. — The  so-called  iodide  of  starch  is  no  chemical 
compound ;  it  has  been  stated  to  be  decomposed  when  heated ;  this 
depends  on  the  affinity  of  warm  water  for  iodine  being  greater  than 
