352       ON  THE  MOVEMENTS  OF  FLUIDS  IN  POROUS  BODIES. 
characterized  condition,  is  precipitated  and  may  be  collected 
and  weighed.  The  arsenic  present  in  the  soil  before  referred  to 
was  estimated  by  this  process,  the  precipitated  sulphide  being 
dissolved  in  ammonia,  the  solution  evaporated  to  dryness,  and 
the  residue  weighed.  The  residue  remaining  in  the  retort  did 
not  contain  a  trace  of  arsenic. 
This  process  also  serves  for  the  detection  of  arsenic  in  the 
presence  of  certain  metallic  compounds  which  interfere  with  the 
action  of  Marsh's  process,  such  as  the  salts  of  copper  and 
mercury,  in  the  presence  of  which  no  arseniuretted  hydrogen  is 
formed.  The  author  states  that  the  presence  of  bismuth  does 
not  at  all  detract  from  the  delicacy  of  Marsh's  test. 
When  oxidizing  salts,  such  as  chlorate  or  nitrate  of  potash, 
are  present,  which  impede  the  action  of  this  test,  the  author 
recommends  their  reduction  by  means  of  bisulphite  of  soda,  the 
excess  of  sulphurous  acid  being  afterwards  driven  off  by  heat. — 
London  Pharm.  Journ.  Jan.  1860. 
ON  THE  MOVEMENTS  OF  FLUIDS  IN  POEOUS  BODIES. 
Among  the  topics  of  scientific  interest  which  awaken  atten- 
tion at  present,  is  the  research  of  Jamin,  professor  at  the  ficole 
Polytechnique,  upon  the  equilibrium  and  movement  of  fluids  in 
porous  bodies.  The  new  results  at  which  he  has  arrived  afford 
an  explanation  of  the  ascent  of  the  sap  in  vegetables  without  the 
necessity  of  recourse  to  the  vital  force.  It  is  apparently  a  ques- 
tion of  capillarity  only. 
Jamin  has  applied  the  new  facts  which  he  has  discovered  to 
the  construction  of  an  apparatus  composed  entirely  of  inorganic 
materials,  but  showing  in  its  structure  a  great  analogy  with 
vegetables.  This  apparatus  has  the  property  of  raising  water  as 
trees  do,  to  a  height  greater  than  that  attained  by  means  of  at- 
mospheric pressure,  from  a  moist  soil,  whence  the  water  is  con- 
stantly drawn  to  the  factitious  leaves  where  it  is  continually  evap- 
orated. 
Reduced  to  its  most  simple  form  this  apparatus  is  composed 
of  a  block  of  some  well  dried  porous  substance,  as  chalk,  litho- 
graphic stone,  &c,  or  a  porous  battery  cell  filled  with  a  powder 
well  rammed  in,  white  chalk  for  instance,  oxyd  of  zinc,  or  even 
