458 
FACTS  RELATING  TO  MAGNESIUM. 
perience  teaches  us  in  this  case  that  if  the  theory  is  favorable 
the  practice  leaves  much  to  be  desired. 
Every  chemist  knows  how  rapid  and  complete  in  some  cases 
is  the  precipitation  of  one  metal  by  another  in  saline  solutions. 
Several  toxicologists,  struck  by  the  precision  of  this  mode  of 
precipitation  and  its  ease  of  execution,  have  proposed  its  use  in 
the  toxicological  researches  of  certain  metals.  We  will  limit 
our  examples  to  the  precipitation  of  arsenic  by  copper,  (Reinsch's 
process),  of  mercury  by  tin  or  by  copper,  of  copper  by  iron  or 
by  zinc,  of  antimony  by  tin,  &c.  These  different  experiments 
present  two  serious  difficulties,  to  mention  which  will  justify  our 
remarks9: — 
1.  The  search  for  every  poisonous  metal  requires  a  distinct 
operation  and  the  employment  of  a  different  metal  for  precipita- 
tion ;  hence  the  necessity  for  numerous  manipulations,  and  the 
considerable  loss  of  the  matters  used  in  the  experiments  which 
these  successive  analyses  necessitate. 
2.  The  introduction  into  the  liquids  under  analysis  of  metals 
either  poisonous  themselves,  such  as  copper  and  zinc,  or  expen- 
sive ones,  such  as  tin,  presents  grave  dangers,  and  it  may  in  some 
cases  render  the  operation  impossible,  even  to  the  expert  chemist, 
if  the  poisoning  is  not  precisely  determined  by  the  metal  em- 
ployed as  the  agent  of  precipitation,  and  which  is  partly  dissolved 
in  the  liquids  under  analysis. 
Were  there  a  metal  completely  destitute  of  poisonous  proper- 
ties which  the  chemist  might  fearlessly  introduce  in  excess  into 
his  liquids,  and  which  had  the  property  of  precipitating  all  the 
metals  whose  salts  are  used  by  poisoners  or  which  might  occa- 
sion accidents,  there  is  no  doubt  but  that  such  a  metal  would 
enormously  facilitate  the  researches  of  legal  chemistry.  Now  it 
seems  to  us  that  magnesium  offers  all  these  advantages,  and  may 
thus  be  of  the  greatest  service. 
There  are  now  prepared  and  offered  to  commerce  great 
quantities  of  nearly  pure  magnesium.  The  original  materials 
and  the  processes  of  its  manufacture  quite  drive  out  of  its  com- 
position the  poisonous  materials  most  dreaded  by  chemists — cop- 
per, lead,  mercury,  antimony,  arsenic,  .zinc,  &c.  It  is  drawn 
into  long  slight  ribbons  well  fitted  for  the  delicate  experiments 
