424  PARCHMENT-PAPER. 
exposed  to  a  mixture  of  two  parts  of  concentrated  sulphuric  acid 
(s.  g.  1.854,  or  thereabouts)  with  one  part  of  water,  for  no  longer 
time  than  is  taken  up  in  drawing  it  through  the  acid,  it  is  imme- 
diately converted  into  a  strong,  tough,  skin-like  material.  All 
traces  of  the  sulphuric  acid  must  be  instantly  removed  by  care- 
ful washing  in  water.  If  the  strength  of  the  acid  much  exceeds 
or  falls  short  of  these  limits,  the  paper  is  either  charred,  or  else 
converted  into  dextrine.  The  same  conversion  into  dextrine  also 
ensues,  if  the  paper  be  allowed  to  remain  for  many  minutes  in 
the  sulphuric  acid  after  the  change  in  its  texture  has  been 
effected. 
In  a  little  more  then  than  a  second  of  time,  a  piece  of  porous 
and  feeble  unsized  paper  is  thus  converted  into  the  Parchment- 
paper,  a  substance  so  strong,  that  a  ring  seven-eights  of  an  inch 
in  width,  and  weighing  no  more  than  23  grains,  sustained  92 
lbs. ;  a  strip  of  parchment  of  the  same  dimensions  supporting 
about  56  lbs.  Though,  like  animal  parchment,  it  absorbs  water, 
water  does  not  percolate  through  it.  Though  paper  contracts  in 
dimensions  by  this  process  of  conversion  into  Parchment-paper, 
it  receives  no  appreciable  increase  of  weight,  thus  demonstrating 
that  no  sulphuric  acid  is  either  mechanically  retained  by  it,  or 
chemically  combined  with  it.  It  has  also  been  ascertained  by 
analysis,  that  no  trace  of  sulphur  exists  in  the  Parchment  paper. 
The  fact  of  this  paper  retaining  its  chemical  identity,  constitutes 
an  important  distinction  between  it  and  the  gun-papers  of  Pelouze 
and  others.  Unlike  those  substances,  it  is  neither  an  electric, 
nor  more  combustible  than  unconverted  paper  of  equal  size  and 
weight,  nor  soluble  in  ether  or  potash.  Unlike  common  paper, 
it  is  not  disintegrated  by  water ;  unlike  common  parchment,  it 
is  not  decomposed  by  heat  and  moisture.  In  this  remarkable 
operation,  the  action  of  the  sulphuric  acid  may  be  classed  among 
the  phenomena  ascribed  to  catalysis  (or  contact  action).  It  is, 
however,  conceivable  that  this  acid  does  at  first  combine  with  the 
woody  fibre,  with  or  without  the  elimination  of  oxygen  and  hy- 
drogen, as  water  ;  and  that  this  compound  is  subsequently  decom- 
posed by  the  action  of  water  in  mass,  during  the  washing  process, 
the  sulphuric  acid  being  again  replaced  by  an  equivalent  of  water ; 
for  as  has  been  before  stated,  the  weight  of  the  paper  remains 
the  same  before  and  after  its  conversion.    Mr.  Warren  de  la 
