VEGETABLE  PARCHMENT  PRESERVE  COVERINGS. 
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and  yielding  and  can  be  readily  stretched  and  tied  over  the  jar. 
As  evidence  of  its  fitness  for  covering  preserves  we  need  simply 
mention  that  since  the  year  1859  nearly  six  millions  pots  have 
been  covered  with  it  by  one  firm  alone.  Vegetable  parchment  is 
merely  unsized  paper  in  which  a  remarkable  physical  alteration 
has  been  induced  by  the  action  of  diluted  sulphuric  acid.  Its 
formation  appears  to  have  been  first  noticed  in  1847  by  Pouma- 
rede  and  Figuier,  who  gave  to  the  altered  paper  the  name  of 
papt/rin.  The  discovery  remained,  however,  without  practical 
application  until  the  year  1857,  when  it  was  patented  in  this 
country  by  Mr.  W.  E.  Gaine,  a  gentleman  whose  attention  had 
for  many  years  been  directed  to  the  improvement  of  paper  used 
for  photographic  and  other  technical  purposes.  The  material 
was  named  by  Mr.  Gaine  vegetable  parchment  or  parchment 
paper,  and  is  now  manufactured  on  a  large  scale  by  Messrs. 
De  la  Rue  k  Co.  To  insure  the  conversion  of  the  soft  unsized 
paper — which  is  familiarly  known  as  blotting-paper,  and  tech- 
nically as  water-leaf — into  a  tough  material  resembling  animal 
parchment,  many  precautions  are  requisite.  The  sulphuric  acid 
by  which  this  strange  conversion  is  effected  must  be  of  a  certain 
strength,  for  if  it  be  too  weak  the  paper  is  dissolved,  and  if  too 
strong  it  is  charred.  The  proper  degree  of  dilution  is  attained 
by  mixing  ordinary  sulphuric  acid  of  sp.  gr.  1*845  with  half  its 
bulk  of  water.  On  passing  the  blotting-paper  or  water-leaf 
into  this  diluted  acid,  it  is  converted  in  a  few  seconds  into  a 
gelatinous  gummy  sheet.  This,  on  being  passed  into  water,  in 
order  to  remove  the  adhering  acid,  becomes  within  a  minute,  a 
tough,  elastic,  skin-like  substance,  which,  when  thoroughly  freed 
from  acid,  is  the  vegetable  parchment  of  commerce.  Freedom 
from  acid  is  insured  by  repeated  washings  in  water,  and  by  im- 
mersion in  a  weak  solution  of  ammonia,  which  converts  any 
slight  trace  of  acid  that  may  remain  into  amnionic  sulphate. 
The  most  curious  fact  connected  with  the  formation  of  the  vege- 
table parchment  is  that  the  chemical  composition  of  the  paper 
and  of  the  sulphuric  acid  remains  unchanged.  The  paper  gains 
nothing  and  loses  nothing,  and  if  submitted  to  chemical  analysis 
after  conversion  into  parchment,  it  is  found  to  have  the  exact 
composition  that  it  had  originally.    The  change  is  therefore 
