462  boussingalt's  researches  on  the  action  of  foliage. 
perish  in  unmixed  carbonic  acid,  apparently  without  decomposing 
any  of  it.  Boussingault  made  his  experiments  in  a  better  form, 
upon  leaves  only,  avoiding  all  complication  of  the  action  of  the 
roots  or  other  parts  of  the  plant.    His  results  are  : 
1.  That  leaves  exposed  to  sunshine  in  pure  carbonic  acid  do 
not  decompose  this  gas  at  all,  or  only  with  extreme  slowness. 
2.  But  in  a  mixture  with  atmospheric  air,  they  decompose  car- 
bonic acid  rapidly.  The  oxygen  of  the  atmospheric  air,  however, 
appears  to  play  no  part. 
3.  Leaves  decompose  carbonic  acid  in  sunshine  as  readily  when 
this  gas  is  mixed  with  nitrogen  or  with  hydrogen. 
Although  this  decomposition  of  carbonic  acid  by  green  foliage 
must  be  a  case  of  dissociation, — a  separation  of  carbon  from 
oxygen, — yet  Boussingault  recognizes  an  analogy  here  with  an 
opposite  phenomenon,  viz.,  with  the  slow  combustion  of  phospho- 
rus at  the  ordinary  temperature.  Phosphorus  in  pure  oxygen 
emits  no  light,  does  not  sensibly  undergo  combustion,  but  does  so 
in  a  mixture  of  oxygen  with  atmospheric  air,  or  with  nitrogen, 
hydrogen,  or  carbonic  acid.  The  analogy  may  even  be  carried 
farther.  For  whil^  a  stick  of  phosphorus  is  not  phosphorescent 
in  pure  oxygen  at  ordinary  or  increased  pressure,  it  becomes  so 
in  rarified  oxygen.  And  Boussingault  equally  ascertained  that 
leaves  which  exerted  no  sensible  action  upon  pure  carbonic  acid 
at  ordinary  pressure,  decomposed  it,  with  the  liberation  of  oxygen 
gas,  under  diminished  pressure.  That  is,  rarefaction  and  mix- 
ture with  an  inert  gas  act  alike  in  mechanically  separating  the 
atoms,  whether  of  carbonic  acid  as  in  the  one  case,  or  of  oxygen 
as  in  the  other,  so  as  to  determine  the  action  either  of  combina- 
tion or  of  dissociation. 
In  a  continuation  of  these  investigations  (Comptes  Mendus, 
vol.  lxi.  Sept.  25,  1865),  Boussingault  shows  that  carbonic  oxide, 
whether  pure  or  diluted,  is  not  decomposable  by  foliage,  and 
that  this  inertness  of  green  foliage  upon  carbonic  oxide  goes  to 
confirm  the  opinion  maintained  in  his  Economie  Rurale,  that 
leaves  simultaneously  decompose  carbonic  acid  and  water,  CO2, 
HO=CO,H,02;  the  O2  being  liberated,  CO,H  expresses  the 
relation  under  which  carbon  is  united  with  the  elements  of  water 
V 
