AmApru,fS93.rm*}       Behavior  of  Metals  with  Gases.  177 
hydrogen  was  passed  over  the  heated  metal.  The  metal  was  used 
as  palladium  black.  Hydrogen  was  absorbed  to  the  extent  of 
502-35  times  the  volume  of  the  metal. 
Platinum  was  examined  as  platinum  sponge  and  platinum  black. 
The  latter  acts  more  energetically,  is  raised  to  redness  by  absorption 
without  the  application  of  external  heat,  as  is  palladium  by  the 
absorption  of  oxygen.  Platinum  sponge  occludes  49*30  times  its 
volume  of  hydrogen.  This  figure  varies  considerably  from  that 
found  by  Graham.  For  an  explanation  of  this  difference  we  must 
refer  to  the  original. 
Gold  occludes  relatively  much  hydrogen  ;  the  action  of  oxygen 
upon  the  metal  charged  with  hydrogen  is  not  very  strong.  In  two 
experiments  there  were  obtained,  respectively,  46-32  and  37-31  times 
the  volume  of  the  metal.  Here  also  the  values  were  decidedly  higher 
than  those  ascertained  by  Graham.  The  latter  used  gold  from 
so-called  assay-rolls,  whilst  the  authors  employed  a  preparation 
obtained  by  precipitating  the  chloride  with  oxalic  acid. 
Silver  absorbs,  according  to  the  author's  experiments,  no  hydro- 
gen, whilst,  according  to  Graham,  silver  wire  occludes  o-2ii  times 
its  volume.  Aluminum  absorbs  2-72  times  its  volume  of  hydrogen 
in  thin  sheets  previously  purified. 
Iron  in  a  state  of  fine  division  absorbs  19-17  times  its  volume- 
Copper  occludes  about  four  and  a  half  times  its  volume. 
Nickel,  which  in  its  chemical  properties  is  intermediate  between 
copper  and  iron,  behaves  similarly  in  its  occlusive  power  for  hydro- 
gen.   It  occludes  17*57  volumes. 
The  absorption  of  hydrogen  by  cobalt  is  rather  large,  and  the 
metal  when  charged  with  hydrogen  becomes  incandescent  in  a  cur- 
rent of  oxygen. 
The  occlusive  power  of  some  metals  for  hydrogen  decreases  on  a 
repetition  of  the  experiments.  The  authors  explain  this  in  the  noble 
metals  by  an  increase  of  density.  This  occurs  according  also  to 
Graham.  Copper  and  nickel  on  a  repetition  of  the  experiment 
show  the  same  occlusive  power.  In  the  case  of  iron  and  cobalt, 
which  behave  like  the  noble  metals,  the  authors  have  not  yet  found 
any  explanation. 
Neumann  has  examined  the  behavior  of  the  precious  metals  with 
oxygen  by  a  method  analogous  to  that  above  described. 
The  metals  were  ignited  for  some  hours  in  pure  oxygen,  two  cal- 
