TRANSFORMATION  OF  SOLUBLE  INTO  INSOLUBLE  GUMS.  565 
When  powdered  gum  Arabic  is  heated  to  100°  C.  (212°F.),  a 
certain  quantity  of  water  is  removed  from  it,  and  its  composition 
may  then  be  represented  by  the  formula  C12EuOu.  At  120QC. 
(248°F.),  it  loses  another  equivalent  of  water,  and  becomes 
isomeric  with  very  dry  starch,  C12H10O10.  In  this  state  it  has 
experienced  no  change  in  its  nature  ;  it  is  still  entirely  soluble 
in  water,  with  the  exception  of  a  slight  calcareous  deposit  which 
precipitates  from  its  solutions.  But  when  the  temperature  of 
120°C.  (9*&°F.)  is  exceeded,  and  that  of  150PC.  (302°F.) 
reached,  or  if  it  be  only  continued  for  a  longtime,  it  is  remarked 
that  almost  the  whole  of  the  gum  loses  its  solubility,  and  is  con- 
verted into  a  mucilaginous  matter,  insoluble  in  cold  water.  This 
reaction  is  effected  without  loss  of  water,  as  I  ascertained  by 
weighing  several  times  the  flask  in  which  I  heated  the  dried  gum  ; 
and  it  is  quite  comparable  to  that  which  converts  starch  and 
soluble  starch  into  dextrine. 
To  obtain  the  perfectly  colorless  product,  several  precautions 
must  be  taken.  It  must  not  be  heated,  for  gum  is  very  rapidly 
colored  by  the  action  of  fire.  At  the  temperature  of  150°C. 
(302°F.),  the  parts  nearest  to  the  metallic  bath  or  the  oil  bath 
are  perceptibly  yellow,  but  the  centre  of  the  mass  has  been 
modified  without  coloration. 
Gum  thus  treated  is  insoluble  in  cold  water,  and  it  is  separated, 
by  means  of  this  liquid,  from  that  which  has  not  been  altered. 
It  swells  up  in  cold  water  much  less  than  tragacanth,  but  quite 
as  much  as  the  cerasine  extracted  from  the  gum  of  this  country. 
When,  instead  of  heating  gum  Arabic  in  powder,  we  heat  it  in 
pieces,  the  product  obtained  acts  in  water  like  the  gums  of  cherry 
and  apricot  trees,  &c,  from  which  it  would  be  very  difficult  to 
distinguish  them. 
In  presence  of  these  characters,  we  are  tempted  to  admit  the 
identity  of  the  two  matters,  especially  when  we  reflect  that  the 
metamorphosis  which  forms  the  subject  of  this  note  is  produced 
without  loss  of  water,  and  that  cerasine  and  arabine  have  exactly 
the  same  composition  in  hundredths. 
Be  this  as  it  may,  modified  gum,  or  artificial  cerasine,  has  all 
the  known  properties  of  the  mucilage  of  Berzelius. 
Treated  with  nitric  acid,  it  furnished  me  an  abundant  crys- 
