boussingalt's  researches  on  the  action  of  foliage.  461 
There  is  one  more  important  observation,  the  omission  of 
which  would  not  fail  to  call  forth  criticism — the  magnesium  which 
contains  silicium  gives  off  on  contact  with  acids  siliciuretted  hydro- 
gen, which  decomposes  at  a  dull  red  heat  like  arseniuretted  and 
antimoniuretted  hydrogens,  leaving  a  dark  brown  deposit.  The 
formation  of  this  deposit  might  give  rise  to  an  error.  Such  is 
the  objection.    A  few  words  will  answer  it : — 
1.  The  magnesium  which  is  now  manufactured  gives  no  foreign 
deposit  in  Marsh's  apparatus  ;  no  sample  of  magnesium  ribbon 
(as  it  is  made  for  burning)  tested  by  us  has  given  either  rings  or 
spots.  The  hydrogen  it  gives  on0  has  always  appeared  remark- 
ably pure  and  inodorous  ;  its  flame  is  hardly  visible. 
2.  Marsh's  apparatus  fed  by  magnesium  is  tested  under  pre- 
cisely the  same  conditions  as  when  fed  by  zinc.  The  suspected 
liquids  are  only  introduced  into  the  apparatus  after  the  prelimi- 
nary verification  of  the  gas-producing  agents. 
3.  The  deposit  of  silicium  left  in  the  red-hot  tube  by  the 
passage  for  the  hydrogen,  accidentally  charged  with  siliciuretted 
hydrogen,  is  moreover  clearly  distinguishable  from  the  deposits 
of  arsenic  and  antimony.  $ 
These  last  two  disappear  immediately  on  contact  with  a  drop 
of  nitric  acid  or  aqua  regia  ;  the  ring  and  spot  of  arsenic  disap- 
pear suddenly  when  touched  with  a  diluted  solution  of  a  hypo- 
chlorite. These  three  tests  have  no  effect  on  the  deposits  of 
silicium  produced  in  the  tube  of  the  Marsh's  apparatus. — Lond. 
Chem.  News,  July  20,  1866,  from  Journ.  de  JPharmacie  et  de 
Chimie,  iii.,  413. 
BOUSSINGAULT'S    RESEARCHES    ON    THE    ACTION  OF 
FOLIAGE. 
A  fall  abstract  of  the  first  part  of  these  investigations,  com- 
municated to  the  French  Academy  of  Sciences,  is  given  in  the 
Comptes  Hendus,  vol.  lx.  No.  18  (May,  1865).  Theodore  Saus- 
sure  had  long  ago  ascertained  that,  while  plants  prosper  and  de- 
compose carbonic  acid  gas  in  an  atmosphere  containing  as  much 
as  one-twelfth  or  even  one-eighth  part  of  that  gas,  they  promptly 
