REDUCTION  OF  IRON  BY  HYDROGEN.  139 
spiration  of  air  charged  with  essential  oil  in  apartments  newly 
varnished.  On  the  other  land,  we  know  how  unfit  water  which 
has  not  been  aerated  is  for  good  alimentation — Ibid,  from 
Comptes  Bendus,  Sept.  24,  1855. 
ON  THE  REDUCTION  OF  IRON  BY  HYDROGEN. 
By  Prof.  Woehler. 
(Translated  by  J.  M.  Maisch.) 
To  obtain  an  oxide  of  iron  suitable  for  the  process  of  reduc- 
tion by  hydrogen,  Woehler  follows  a  way  proposed  by  Faraday  for 
obtaining  a  good  polishing  powder.  Pure  sulphate  of  iron  (green 
vitriol)  which  needs  not  to  be  exsiccated,  is  mixed  with  pure  table 
salt,  (two  or  three  times  the  weight  of  the  anhydrous  vitriol) 
and  in  a  Hessian  crucible  heated  to  redness,  and  melted.  After 
cooling  and  washing  with  water,  oxide  of  iron  remains  behind 
in  dark  red,  shining  scales.  By  this  process  some  iron  is  lost 
by  the  sublimation  of  some  chloride,  which  however  is  insignifi- 
cant, considering  the  cheapness  of  the  material.  This  oxide  is 
then  introduced  into  a  clean  gun-barrel  or  glass-tube,  which,  if 
necessary,  may  be  surrounded  by  a  layer  of  clay.  The  hydro- 
gen must  be  dried  by  chloride  of  calcium  or  sulphuric  acid ; 
crude  oil  of  vitriol  may  be  purified  by  Buckner's  method  (Amer. 
Journ.  Ph.,  1855,  417)  from  all  arsenic,  which  otherwise  would 
be  taken  up  by  the  iron,  rendering  it  unfit  for  medical  use.  It  is, 
however,  without  any  influence  on  the  purity  of  the  iron,  if 
hydrogen  be  evolved  by  iron,  (wire  or  nails,)  instead  of  by  zinc, 
in  which  case  the  pure  sulphate  of  iron  will  at  the  same  time 
be  obtained. 
After  the  atmosperic  air  is  expelled  from  the  apparatus,  the 
pipe  is  heated  to  redness,  and  the  current  of  hydrogen  is  con- 
tinued until  water  ceases  to  escape  on  the  open  end  of  the  tube ; 
the  apparatus  is  then  allowed  to  cool  before  the  iron  is  taken 
out,  otherwise  it  will  take  fire  and  burn.  The  reduced  iron  ap- 
pears in  thin  grey  scales,  pseudo-morphoses  of  the  crystals  of 
the  oxide ;  they  are  porous,  and  may  be  easily  reduced  to  the 
finest  powder,  which  is  light  grey,  without  lustre,  catches  fire 
and  dissolves  in  diluted  sulphuric  acid,  without  leaving  a  residue. 
