PRODUCTION  OP  MANNITE  BY  MARINE  PLANTS. 
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Some  botanists  have  thought  that  the  production  of  mannite, 
by  marine  plants,  was  in  consequence  of  a  secretion  of  the  sub- 
stance in  question  by  the  living  plant ;  but  I  have  proved  that 
this  saccharine  matter  is  only  produced  after  the  vital  activity 
of  the  plant  has  ceased.  Moreover,  my  observations  on  this 
point  lead  me  to  believe,  that  the  production  of  mannite  is  always 
the  result  of  a  peculiar  kind  of  fermentation,  which  disoxidises 
the  vegetable  mucilage  and  transforms  it  into  mannite. 
We  know  that  many  of  the  marine  algae  contain  such  large 
quantities  of  mucilage,  that  some  naturalists  have  tried  to  render 
this  production  useful  as  a  manufacture.  For  instance,  Mr. 
Brown  has  found  that  prolonged  boiling  with  dilute  sulphuric 
acid  suffices  to  convert  this  substance  into  arabine  (gum  arabic). 
I  have  obtained  very  large  quantities  of  mannite  after  remov- 
ing the  algae  from  the  water,  by  placing  them  still  moist  between 
sheets  of  grey  paper,  so  that  the  access  of  air  is  not  prevented, 
and  leaving  them  there  for  eight  days.  At  the  end  of  this  time, 
the  surface  is  covered  with  an  efflorescence  of  mannite.  It  is  in 
this  case  formed  more  in  the  shape  of  grains  than  in  crystals, 
but  when  dissolved  in  water,  such  as  is  furnished  by  the  plant, 
it  crystallises,  by  the  evaporation  of  the  liquid,  in  long,  acicular 
and  colorless  tufts. 
I  account  for  its  production  in  the  following  manner : — 
Supposing  that  the  mucilage  has  the  formula  attributed  to  it, 
C12  H16  O10,  and  which  represents  the  composition  of  this  sub- 
stance dried  in  vacuo  at  180°  C.  (266°  F.),  we  find  that  in  the 
presence  of  water  and  losing  one  equivalent  of  oxygen,  it  may  be 
divided  into  two  equivalents  of  mannite ;  thus — 
CM  H10  O10+4  HO=2  C6  H7  06+0 
Veg.  mucilage+water==mannite+oxygen. 
It  is,  consequently,  by  means  of  a  disoxidising  influence  ex- 
erted on  the  mucilage,  that  mannite  is  produced.  This  substance 
is  likewise  produced  during  viscid  fermentation,  as  is  well  known, 
in  which  case  a  viscid  matter  is  formed  of  the  Dature  of  the  gums 
(in  wine,  beer,  and  vegetable  juices  as  they  spoil),  and  in  these 
circumstances  the  mannite  produced,  proceeds  evidently  from 
the  disoxidising  action  which  the  fermenting  matter  exercises  on 
this  viscid  substance. 
I  have  often  observed,  that  the  intercellular  mucilage  of  ma- 
