magnesium:  its  preparation  and  properties.  283 
for  excluding  all  traces  of  sulphuric  acid.  The  reason  for  par- 
ticularity in  this  respect  is,  that  the  sodium  used  afterwards  for 
reducing  magnesium  from  the  chloride  would  likewise  take  away 
oxygen  from  the  sulphuric  acid,  thereby  giving  rise  to  the  pro- 
duction of  sulphides,  which  are  found  to  materially  hinder  the 
aggregation  of  the  small  globules  of  reduced  magnesium.  Mr. 
Sonstadt  preferably  used  chloride  of  potassium  for  adding  to  the 
solution  of  the  chloride  of  magnesium  prepared  as  already  men- 
tioned. The  compound  solution  is  then  evaporated  to  dryness, 
and  the  solid  residue  placed  in  a  platinum  crucible  of  sufficient 
size  ;  heat  is  then  applied  until  the  salt  has  perfectly  melted, 
and  any  particles  of  infusible  matter  have  had  time  to  subside. 
The  fused  salt  is  poured  out  carefully  on  an  iron  plate  ;  it 
quickly  solidifies,  and  should  then  be  broken  up  and  preserved 
in  stoppered  bottles  until  required  for  use  in  the  subsequent  steps 
of  the  process. 
Before  leaving  the  consideration  of  the  first  part  of  the  pro- 
cess, we  may  quote  the  following  words  from  Mr.  Sonstadt's 
specification,  as  they  convey  a  hint  to  our  readers  regarding  the 
selection  of  specimens  of  magnesium  wire  : — "When  the  material 
from  which  magnesium  is  to  be  prepared  contains  ammonium, 
in  whatever  state  of  combination,  the  metal  obtained  from  it 
invariably  contains  nitrogen,  the  presence  of  which  causes  the 
magnesium  to  have  a  yellow  color,  and  to  tarnish  rapidly  in  the 
atmosphere."  It  might  be  added  to  this  that  the  regularity  of 
combustion  of  even  thin  wire  seems  to  be  decidedly  interfered 
with  by  the  same  circumstance. 
II. — The  Reduction  of  Magnesium  from  its  Chloride. 
The  magnesium  now  manufactured  on  the  large  scale  is  almost 
exclusively  obtained  by  the  action  of  metallic  sodium  on  the 
chloride  of  magnesium ;  or,  what  amounts  to  the  same,  of  the 
double  salt  previously  referred  to.  there  are,  however,  other 
modes  of  reducing  the  chloride,  the  most  interesting  and  simple 
of  which  will  be  hereafter  described.  In  order  to  obtain  mag- 
nesium with  the  aid  of  sodium,  one  part  of  the  latter,  cut  into 
small  pieces,  is  placed  in  an  iron  crucible,  and  covered  with  five 
parts  of  the  double  chloride  of  magnesium  and  potassium  ;  the 
cover  of  the  crucible  is  now  put  on,  and  the  temperature  of  the 
