4 
ON  THE  PREPARATION  OF    LIQUID  GLUE.  17 1 
NOTE  ON  THE  PREPARATION  OF  LIQUID  GLUE. 
By  M.  S.  Dumodlin. 
All  chemists  are  aware,  that  when  a  solution  of  glue  (gelatine) 
is  heated  and  cooled  several  times  in  contact  with  the  air,  it  loses 
the  property  of  forming  a  jelly.  M.  Gmelin  observed,  that  a  solu- 
tion of  isinglass,  enclosed  in  a  sealed  glass  tube  and  kept  in  a 
stale  of  ebullition  on  the  water-bath  for  several  days,  presented 
the  same  phenomenon,  that  is  to  say,  the  glue  remained  fluid, 
and  did  not  form  a  jelly. 
The  change  thus  produced  is  one  of  the  problems  most  difficult 
of  solution  in  organic  chemistry.  It  may  be  supposed,  however, 
that  in  the  alteration  which  the  glue  undergoes,  the  oxygen  of  the 
air  or  of  the  water  plays  a  principal  part  ;  what  leads  me  to  think 
this  is  the  effect  produced  upon  glue  by  a  small  quantity  of  nitric 
acid.  It  is  well  known,  that  by  treating  gelatine  with  an  excess 
of  this  acid,  it  is  converted  by  heat  into  malic  and  oxalic  acids, 
fatty  matter,  tannin,  &c.  But  it  is  not  thus  when  this  glue  is 
treated  with  its  weight  of  water  and  with  a  small  quantity  of 
nitric  acid  ;  by  this  means  a  glue  is  obtained  which  preserves 
nearly  all  its  primitive  qualities,  but  which  has  no  longer  the 
power  of  forming  a  jelly.  Upon  this  process,  which  I  communi- 
cated, is  founded  the  Parisian  manufacture  of  the  glue  which  is 
sold  in  France  under  the  title  of  "  colle  liquide  et  inalterable'1 
This  glue  being  very  convenient  for  cabinet-makers,  joiners, 
pasteboard-workers,  toy  makers,  and  others,  as  it  is  applied  cold,  I 
think  it  my  duty,  in  order  to  increase  its  manufacture,  to  publish 
the  process. 
It  consists  in  taking  1  kilogrm.  [2  and  l-5th  lbs.]  of  glue,  and 
dissolving  it  in  1  litre  [2  and  l-9th  pts.]  of  water  in  a  glazed  pot 
over  a  gentle  fire,  or  what  is  better,  in  the  water-bath,  stirring  it 
from  time  to  time.  When  all  the  glue  is  melted,  200  grms.  [7  oz. 
Av.]  of  nitric  acid  (spec.  grav.  1*32)  are  to  be  poured  in,  in  small 
quantities  at  a  time.  This  addition  produces  an  effervescence, 
owing  to  the  disengagement  of  hyponitrous  acid.  When  all  the 
acid  is  added,  the  vessel  is  to  be  taken  from  the  fire,  and  left  to  cool. 
I  have  kept  the  glue,  thus  prepared,  in  an  open  vessel  during 
more  than  two  years,  without  its  undergoing  any  change.  It  is 
very  convenient  in  chemical  operations ;  I  use  it  with  advantage 
