ON  CELLLULOSE  AND  THE  COMPOSITION  OF  WOOD.  75 
To  obtain  the  ligneous  vessels  in  a  state  of  purity,  entirely  free 
from  fibrous  or  utricular  substance,  the  wood  was  treated  first 
with  dilute  potash,  which  removed  the  tannin,  albuminous  and 
pectic  matters.  It  was  then  submitted  to  the  action  of  hydro- 
chloric acid,  commencing  with  dilute,  and  gradually  changing 
it  for  stronger,  until  the  fuming  acid  was  employed.  By  this 
means  the  utricular  tissue  was  partly  dissolved,  and  the  ligneous 
fibres  rendered  soluble  in  the  cupric  reagent.  In  the  last  place, 
this  tissue  is  treated  with  cold  concentrated  sulphuric  acid,  then 
washed  with  water,  alcohol,  and  ether.  In  this  way  the  ligneous 
vessels  are  obtained  perfectly  pure.  The  substance  of  which 
these  vessels  are  formed  M.  Fremy  distinguishes  by  the  name 
of  vasculose.  It  is  characterized  by  its  insolubility  in  hydro- 
chloric acid,  concentrated  of  sulphuric  acid,  and  cuprate  of 
ammonia.  It  is  dissolved,  on  the  contrary,  by  potash,  concen- 
trated and  boiling. 
The  utricular  substance,  which  forms  the  medullary  rays,  is 
identical  with  the  pith.  It  is,  like  it,  insoluble  in  the  cupric 
reagent,  but  rendered  soluble  by  the  action  of  acids,  of  alkalies, 
or  of  heat.  It  consists  of  Para-cellulose,  The  concentrated 
and  boiling  potash,  which  dissolves  the  ligneous  vessels,  can  also 
dissolve  the  medullary  rays  ;  this  solubility  affords  the  means  of 
isolating  the  third  organ  of  the  woody  tissue :  the  ligneous  fibres. 
Chippings  of  wood  are  treated  in  a  glass  flask  with  potash 
sufficiently  strong  and  hot  to  effect  the  disorganisation  of  the 
wood.  It  is  important  not  to  go  beyond  that  point,  as  the 
ligneous  fibres  themselves  may  be  altered.  The  insoluble  por- 
tion is  afterwards  removed,  and  washed  with  water,  alcohol  and 
ether.  It  consists  of  ligneous  fibres,  perfectly  white  and  in  a 
state  of  purity.  Oak  and  deal  were  the  woods  employed  by  M. 
Fremy.  The  substance  forming  these  ligneous  fibres  is  named 
Fibrose ;  it  is  characterized  by  its  insolubility  in  the  alkaline 
solution,  which  dissolves  the  vessels  and  the  medullary  rays ; 
by  its  solubility  in  sulphuric  acid,  which  does  not  dissolve  the 
ligneous  vessels ;  by  its  insolubility  in  the  cupric  reagent,  which 
immediately  dissolves  the  cellulose,  but  does  not  attack  the  lig- 
neous fibres  until  they  are  modified  by  chemical  agents.  Fibrose 
and  cellulose  may  be  also  distinguished  by  the  action  of  sulphuric 
acid,  which  immediately  dissolves  cellulose,  converting  it  into 
