DIFFERENCES  OF  ACTION  BETWEEN  POTASSA  AND  SODA.  553 
and  437°  F.)  for  four  hours;  the  mass  having  become  white,  it  is 
dissolved,  and  a  portion  of  it  is  tested  with  a  salt  of  lime. 
2.  For  other  matters,  it  is  better  to  introduce  them  into  the  liq. 
concentrated  only  to  about  48°  Beaume  (or  1,500  sp.  gr.)  and  to 
evaporate  the  whole  together;  the  ligneous  matter  is  dissolved,  and 
when  the  mass  has  become  thick,  and  is  still  brown,  it  contains 
much  ulmic  acid,  no  oxalic,  acetic,  formic,  or  carbonic  acids ;  the 
hot  mass  is  still  maintained  between  200°  and  225°  C.  (392°  and 
437°  F.);  it  becomes  yellow,  then  whitish,  and  after  being  heated 
for  four  or  five  hours,  it  no  longer  contains  ulmic  acid,  but  all  the 
other  acids  above  mentioned. 
We  may,  indeed,  complete  the  operation  more  rapidly,  but  then 
we  often  destroy  a  portion  of  the  oxalic  acid. 
When  we  substitute  soda  for  potassa,  the  final  reaction  is  not  the 
same ;  when  the  organic  matter  is  dissolved,  we  likewise  find  much 
ulonic  acid  ;  but  by  continuing  to  heat  in  order  to  convert  the  latter 
into  oxalic  acid,  whatever  care  we  may  take,  the  oxalic,  acetic,  and 
formic  acids  appear  to  be  destroyed  as  they  are  formed,  for  however 
long  the  reaction  may  last,  we  can  always  ascertain  their  presence  ; 
but  whenever  it  is  stopped,  and  with  whatever  proportion  of  soda 
we  operate,  we  never  obtain  anything  but  very  small  quantities  of 
oxalic  acid,  or,  on  the  average,  one-tenth  as  much  as  with  potassa, 
often  only  traces,  and  with  certain  matters,  such  as  wool,  silk,  and 
leather,  not  even  traces. 
In  general,  the  presence  of  the  oxalates  appears  very  ephemeral 
in  these  reactions  with  soda,  especially  when  we  operate  on  several 
kilogrammes  of  organic  matter  at  once.  The  more  considerable 
the  mass,  the  more  difficult  the  operation  is  to  conduct ;  with  po- 
tassa this  inconvenience  is  not  at  all  experienced. 
It  seems  that  this  destructive  action  of  hydrate  of  soda  may  be 
attributed  to  its  being  less  fusible  than  hydrate  of  potassa,  and  too 
energetic.  Indeed,  if  we  make  mixtures  of  the  two  hydrates  in  such 
proportions  that  the  mass  shall  retain  nearly  the  same  fusibility  as 
hydrate  of  potassa  alone,  then  the  production  of  oxalic  acid  will  not 
only  not  be  diminished,  but  will  even  be  increased;  certain  propor- 
tions of  soda  increase,  in  this  case,  the  useful  effect  of  potassa,  admit 
of  the  employment  of  larger  proportions  of  organic  rrjatter,  and  of 
thus  obtaining  a  larger  proportion  of  oxalic  acid  with  the  same 
quantities  of  caustic  alkalies. 
