ABSORPTION  AND  DIALYTIC  SEPARATION  OF  GASES,  ETC.  511 
balloon  with  sifted  sawdust.  For  commanding  a  vacuum  in  such 
experiments,  the  air  exhauster  of  Dr.  Hermann  Sprengle*  is 
admirably  adapted.  It  possesses  the  advantage  that  the  gas 
drawn  from  the  vacuum  can  also  be  delivered  by  the  instrument 
into  a  glass  receiver  placed  over  water  or  mercury.  The  "  fall 
tube  "  has  merely  to  be  bent  at  the  lower  end. 
The  surprising  penetration  of  platinum  and  iron  tubes  by  hy- 
drogen gas,  discovered  by  MM.  H.  Sainte-Claire  Deville  and 
Troost,  appears  to  be  connected  with  a  power  resident  in  the 
same  and  certain  other  metals  to  liquefy  and  absorb  hydrogen, 
possibly  in  its  character  as  a  metallic  vapor.  Platinum  in  the 
form  of  wire  or  plate  at  a  low  red  heat  may  take  up  and  hold 
3#8  volumes  of  hydrogen,  measured  cold;  but  it  is  by  palladium 
that  the  property  in  question  appears  to  be  possessed  in  the  high- 
est degree.  Palladium  foil  from  the  hammered  metal,  con- 
densed so  much  as  643  times  its  volume  of  hydrogen,  at  a  tem- 
perature under  100°  C.  The  same  metal  had  not  the  slightest 
absorbent  power  for  either  oxygen  or  nitrogen.  The  capacity  of 
fused  palladium  (as  also  of  fused  platinum)  is  considerably  re- 
duced ;  but  foil  of  fused  palladium,  for  which  I  am  indebted  to 
Mr.  G.  Matthey,  still  absorbed  68  volumes  of  gas.  A  certain 
degree  of  porosity  may  be  admitted  to  exist  in  these  metals,  and 
to  the  greatest  extent  in  their  hammered  condition.  It  is  be- 
lieved that  such  metallic  pores,  and  indeed  all  fine  pores,  are 
more  accessible  to  liquids  than  to  gases,  and  in  particular  to 
liquid  hydrogen.  Hence  a  peculiar  dialytic  action  may  reside 
in  certain  metallic  septa,  like  a  plate  of  platinum,  enabling  them 
to  separate  hydrogen  from  other  gases. 
In  the  form  of  sponge,  platinum  absorbed  1-48  times  its  vol- 
ume of  hydrogen,  and  palladium  90  volumes.  The  former  of 
these  metals,  in  the  peculiar  condition  of  platinum  black,  is  al- 
ready known  to  take  up  several  hundred  volumes  of  the  same 
gas.  The  assumed  liquefaction  of  hydrogen  in  such  circumstan- 
ces appears  to  be  the  primary  condition  of  its  oxidation  at  a  low 
temperature.  A  repellant  property  possessed  by  gaseous  mole- 
cules appears  to  resist  chemical  combination  as  well  as  to  estab- 
*  Chemical  Society's  Journal,  ser.  2,  vol.  iii.  p.  9  (1865.) 
