140 
NEW  RESEARCHES  ON  STARCH. 
slightly  soluble  in  cold  water,  but  nine-tenths  of  it  are  insoluble 
in  that  fluid.  But  if  the  sticky  mixture  of  starch  and  acid  be 
left  to  itself  for  from  forty-eight  to  sixty  hours,  or  heated  until 
the  appearance  of  reddish  vapors,  it  becomes  completely  lique- 
fied, and  the  starch  may  still  be  entirely  separated  by  concen- 
trated alcohol.  The  product,  washed  with  alcohol  to  remove 
adherent  acid,  is  then  completely  soluble  in  cold  water.  In  all 
cases  both  the  soluble  and  insoluble  matters  acquire  a  blue  color 
by  iodine. 
A  thick  mixture  of  starch  and  concentrated  sulphuric  acid, 
SO3  HO,  treated  with  alcohol  after  about  four  minutes  contact, 
behaves  exactly  like  the  mixture  of  starch  and  nitric  acid ;  the 
starch  is  entirely  separated,  and  becomes  partially  soluble  in  cold 
water.  But  when  the  mixture  is  left  for  half  an  hour,  the  starch 
separated  by  the  alcohol  has  become  completely  soluble  in  cold 
water. 
Crystallizable  acetic  acid,  heated  to  212°  F.  with  starch,  in  a 
sealed  tube,  converts  it  into  the  soluble  modification  in  from 
three  to  five  hours ;  the  starch  grains  are  not  deformed  or  dis- 
solved ;  they  are  merely  split  (but  not  exfoliated)  in  the  region 
opposite  to  the  tube.  Ordinary  acetic  acid  acts  more  quickly 
upon  starch,  and  may  convert  it  into  dextrine  under  the  same 
circumstances. 
A  concentrated  solution  of  fused  chloride  of  zinc,  free  from 
acid,  converted  starch  into  a  paste  in  the  cold.  This  paste  lique- 
fies in  a  few  hours  when  heated  to  212°  F.  The  mixture  may 
be  heated  to  284°  F.  without  the  formation  of  any  trace  of  dex- 
trine ;  but  the  starch  separated  from  this  zinc  solution  by  alcohol 
may,  according  to  the  duration  of  the  reaction,  become  entirely 
soluble  in  cold  water. 
Starch  heated  in  a  very  concentrated  solution  of  caustic  potash 
or  soda,  loses  the  whole  of  its  [?]  nitrogen  in  the  form  of  ammo- 
nia. The  author  confirmed  this  evolution  of  ammonia,  not  only 
by  test  paper,  but  also  by  converting  this  alkali  into  the  double 
chloride  of  platinum  and  ammonium.  When  the  caustic  alkali  is 
saturated  with  acetic  acid,  the  addition  of  alcohol  separates  the 
whole  of  the  starch.  A  small  quantity  has  become  soluble,  but 
the  greater  part  remains  insoluble,  not  only  in  cold,  but  even  in 
boiling  water.    Dextrine  is  never  formed  by  the  action  of  caustic 
