284     magnesium:  its  preparation  and  properties. 
whole  rapidly  raised  to  full  redness.  When  the  heat  has  been 
continued  for  a  sufficient  length  of  time,  the  crucible  is  allowed 
to  cool,  and  when  perfectly  cold  the  cover  is  removed  and  the 
contents  extracted.  The  mass  is  now  quickly  washed  with 
water,  which  dissolves  the  saline  matter,  and  leaves  the  reduced 
magnesium  in  the  form  of  small  globules  more  or  less  adherent 
to  each  other.  The  drying  of  the  washed  metal  must  be  accom- 
plished as  rapidly  as  possible,  at  a  temperature  not  higher  than 
the  boiling-point  of  water. 
Another  mode  of  producing  magnesium  has  already  been  re- 
ferred to.  This  consists  in  employing  the  decomposing  power 
of  the  galvanic  current.  This  mode  of  reducing  magnesium 
was  first  successfully  employed  by  Bunsen ;  but  the  following 
instructive  and  simple  experiment  is  due  to  Matthiessen  : — Take 
a  common  clay  tobacco  pipe  with  a  bowl  nearly  globular  in 
shape.  In  the  cavity  of  the  latter  fuse  some  of  the  double 
chloride  of  magnesium  and  potassium  over  a  gas  flame.  When 
the  salt  is  fused  pass  up  the  pipe  stem  a  fine  iron  wire,  and  al- 
low it  to  project  into  the  bowl,  so  as  to  have  its  point  well  below 
the  surface  of  the  fused  salt.  This  wire  should  be  connected 
with  the  negative  pole  of  a  battery  of  about  six  elements,  the 
positive  wire  of  which  is  terminated  by  a  piece  of  gas  coke 
which  is  made  to  just  touch  the  surface  of  the  fused  mass.  De- 
composition at  once  commences,  the  result  of  which  is  the  de- 
position of  minute  globules  of  metallic  magnesium.  This  is  a 
most  interesting  experiment,  and  one  very  easy  performed  with- 
out the  least  danger. 
It  must  be  recollected  that  the  chloride  of  potassium  present 
in  the  double  salt  plays  but  a  mechanical  part,  and  has  not  any- 
thing directly  to  do  in  the  reduction  of  the  metal. 
Ill — Purification  of  the  Metal  by  Distillation. 
The  purification  of  the^metal  by  distillation  is  the  most  cer- 
tain and  effectual  method  which  can  be  adopted,  and  the  inven- 
tion of  the  apparatus  by  means  of  which  this  object  can  bev  ac- 
complished on  the  large  scale  in  an  atmosphere  of  hydrogen  is 
due  to  the  ingenuity  of  Mr.  Sonstadt.  We  may  mention  that 
the  manufacture  of  magnesium  on  the  large  scale,  according  to 
Mr.  Sonstadt's  patents,  is  now  being  extensively  carried  on  by 
