ON  CELLULOSE  AND  THE  COMPOSITION  OF  WOOD.  73 
formed  of  cellulose,  freed  from  organic  incrustations,  but  their 
interior  walls  are  coated  with  a  thin  layer  of  nitrogenous  matter 
containing  traces  of  fat  and  foreign  bodies,  which  oppose  the 
penetration  and  solvent  action  of  the  cupric  reagent.  To  remove 
these  impurities,  the  pith  was  cut  into  slices  and  immersed  in 
the  copper  solution,  by  which  the  cells  were  colored  and  swol- 
len, but  not  dissolved.  The  slices  were  then  removed,  and  im- 
mersed in  cold  water,  acidulated  with  hydrochloric  acid,  which 
slowly  dissolved  the  lime,  &c;  they  were  then  washed  with  pure 
water,  and  upon  again  treating  with  the  cuprate  of  ammonia 
they  readily  dissolved. 
M.  Fremy  considers  that  in  these  experiments  of  M.  Payen, 
the  action  of  the  hydrochloric  acid  and  the  means  employed  to 
remove  the  impurities  are  sufficient  to  effect  a  modification  of 
the  insoluble  cellulose.  He  points  out,  that  tissue  as  dense  as 
vegetable  ivory,  or  impure  as  the  ordinary  cortical  fibres,  is  read- 
ily attacked  by  the  cupric  solution.  He  has  also  shown  that  the 
tissue  of  pith  may  be  rendered  soluble  by  simply  exposing  it  to 
a  temperature  of  150o  cent.,  or  by  boiling  it  in  water  for  twenty- 
four  hours,  in  both  of  which  cases  the  mineral  matter  remains 
unaffected,  the  organic  substance  alone  undergoing  alteration. 
The  tissue,  thus  modified  and  rendered  soluble,  furnishes  upon 
calcination  the  same  amount  of  inorganic  matter,  which  retains 
the  original  form  of  the  tissue,  as  the  original  and  insoluble 
pith. 
M.  Payen  again  brings  forward  the  following  experiments : 
— In  order  to  destroy  the  obstacles  to  solution  which  might  re- 
sult from  the  want  of  contact  and  wetting,  owing  to  the  interpo- 
sition of  air,  the  pith  was  submitted  to  a  simple  grinding  in 
cold  water,  by  which  means  45-100ths  of  the  total  weight  was 
rendered  soluble ;  this  proportion  was  further  increased  to 
75-100ths  by  previously  drying  the  tissue  at  110°  cent,  in  a  va- 
cuum. In  another  case,  the  pith  was  immersed  in  water,  and 
maintained  in  a  vacuum  for  some  time  ;  the  tissue,  thus  gorged 
with  liquid,  was  then  frozen:  when  afterwards  thawed,  and  agi- 
tated with  the  reagent,  it  immediately  commenced  to  dissolve. 
In  this  way  56  per  cent,  of  the  tissue  was  brought  into  solu- 
tion :  the  insoluble  portion  contained  15.5  per  cent,  of  inorganic 
matter.    The  insoluble  part  in  this  experiment,  and  in  the  pre- 
