FACTS  RELATING  TO  MAGNESIUM.  457 
electro-motive  force.  Direct  experiment  confirms  this  theoretical 
inference.  A  small  plate  of  magnesium,  0*1  gr.  in  weight, 
placed  beside  a  plate  of  copper  in  a  small  tube  of  glass  of  six 
centimetres  cube,  filled  with  acidulated  water,  produced  in  nearly 
ten  minutes  an  electro-magnetic  appearance,  and  illuminated  a 
Geisler  tube  10  cent.  long.  If  magnesium  should  ever  become 
cheap,  this  would  decidedly  be  the  best  way  of  producing 
electricity. 
The  preceding  facts  appear  to  us  above  all  to  give  a  special 
interest  to  toxicological  researches  on  metallic  poisons.  A  few 
words  on  the  subject  are  necessary  to  give  a  clear  idea  of  the  im- 
portance of  this  new  application  of  magnesium.  In  all  true 
chemical  researches  respecting  the  diagnosis  and  extraction  of 
compound  metallic  poisons,  the  experimentalist,  after  having  de- 
stroyed the  viscus,  or  any  other  organic  matter  under  his  analy- 
sis, at  last  finds  a  greater  or  less  proportion  of  either  a  saline  or 
an  acid  liquid,  in  which  he  has  to  discover  and  determine  the 
minute  proportions  of  poisonous  metal.  Whatever  the  agent  used 
in  the  destruction  of  organic  matter — whether  sulphuric  acid, 
chlorine,  aqua  regia,  or  nitric  acid — the  ultimate  liquid  is  always 
very  complex.  Over  and  above  the  poisonous  substance  which 
it  may  contain,  there  is  always  a  great  deal  of  soda,  lime,  mag- 
nesia, phosphoric  acid,  hydrochloric  acid,  &c,  &c. ;  and  also  in 
most  cases,  whether  colorless  or  slightly  colored,  it  contains 
some  strictly  organic  substances,  which  are  the  necessary  result 
of  the  action  on  such  energetic  agents  as  chlorine,  aqua  regia, 
and  nitric  acid. 
In  most  cases  it  is  possible  to  find  and  to  separate  the  metal 
which  determines  the  poisoning  by  a  methodic  use  of  such  tests 
as  hydrosulphuric  acid,  hydrosulphate  of  ammonia,  &c.  But  not 
only  do  these  processes,  even  in  the  hands  of  the  most  ex- 
perienced chemists,  offer  but  a  limited  sensibility,  and  are  some- 
times powerless  merely  from  the  effect  of  the  complexity  of  the 
liquid  under  analysis,  but  they  necessitate  the  sacrifice  of  a 
great  quantity  of  the  liquid  in  the  indispensable  preliminary 
researches.  The  use  of  the  pile  recommended  by  eminent  toxi- 
cologists  in  isolating  and  precipitating  poisonous  metals  contained 
in  these  liquids,  has  always  given  us  incomplete  results,  and  ex- 
