FACTS  RELATING  TO  MAGNESIUM. 
459 
of  the  laboratory;  it  keeps  equally  well  in  a  dry  or  moist 
atmosphere,  and  placed  in  a  corked  bottle  it  is  safe  from  any 
alteration  ;  its  low  equivalent  displaces  the  ordinary  poisonous 
metals  by  relatively  small  proportions  of  the  precipitating  metal. 
Magnesium  and  its  compounds  present  no  danger ;  it  is  one  of 
the  metals  normally  contained  in  the  tissues  and  fluids  of  the 
animal  economy,  and  the  introduction  of  them  into  liquids  to  be 
analyzed  does  not  cause  the  least  difficulty.  The  silicium  which 
was  found  in  the  first  samples  manufactured  is  now  seldom  seen  ; 
and  it  is  easy  to  understand  that  the  presence  of  some  thou- 
sandths or  hundredths  of  silicium  or  of  soda  would  be  no 
hindrance  in  the  toxicological  researches  under  discussion.  Let 
us  add  (although  the  consideration  is  of  small  importance  in  such 
serious  analyses)  that  the  price  of  magnesium  is  now  very 
moderate,  and  it  will  no  doubt  become  still  more  so,  should  the 
demand  increase.  A  rapid  sketch  of  the  reactions  produced  by 
the  contact  of  a  plate  of  magnesium  with  the  different  acidulous 
metallic  solutions  does  away  with  any  necessity  for  entering  into 
the  details  of  the  specially  toxicological  operation.  We  will 
merely  give  a  summary. 
The  acid  liquids  obtained  from  the  viscera  or  other  organic 
matters  under  analysis  are  concentrated  by  evaporation  in  a 
water  bath,  and  brought  to  a  syrupy  consistence.  The  residue 
heated  to  125°  is  redissolved  in  a  small  quantity  of  distilled 
water,  then  filtered. 
We  then  arrange  one  of  Marsh's  ordinary  apparatus,  into 
which  we  introduce  some  water  acidulated  with  sulphuric  acid, 
and  some  grammes  of  magnesium  ribbon.  A  considerable  escape 
of  hydrogen  then  takes  place,  which  must  be  carried  through  a 
tube  at  a  red  heat  in  the  middle,  and  ignited  at  the  smaller 
extremity.  If  no  rings  are  formed  on  the  tube,  and  no  spot  on 
the  porcelain  plates  held  upon  the  flame  of  the  gas,  then  suc- 
cessively introduce  into  the  apparatus  small  portions  of  the  sus- 
pected liquid.  If  either  antimony  or  arsenic  is  present  in  the 
liquid,  a  ring  will  not  be  long  in  appearing,  as  in  the  ordinary 
Marsh's  apparatus,  and  the  flame  flattened  against  the  porcelain 
plate  leaves  there  a  shiny  deposit.  The  spots  and  rings  of 
arsenic  are  distinguishable  from  the  spots  and  rings  of  antimony 
