178 
RELATION  OF  HYDROGEN  TO  PALLADIUM. 
to  thousandths.  The  distance  between  two  fine  cross  lines 
marked  upon  the  surface  of  the  "wire  near  each  of  its  extremities 
was  observed. 
ExpL    1. — The  wire  has  been  drawn  from  welded  palladium, 
and  was  hard  and  elastic.    The  diameter  of  the  wire  was  0-462 
millimetre ;  its  specific  gravity  was  12*38,  as  determined  with 
care.    The  wire  was  twisted  into  a  loop  at  each  end,  and  the 
mark  made  near  each  loop.    The  loops  were  varnished  so  as  to 
limit  absorption  of  gas  by  the  wire  to  the  measured  length 
between  the  two  marks.    To  straighten  the  wire,  one  loop  was 
fixed,  and  the  other  connected  with  a  string  passing  over  a 
pully  and  loaded  with  1-5  kilogramme,  a  weight  sufficient  to 
straighten  the  wire  without  occasioning  any  undue  strain.  The 
wire  was  charged  with  hydrogen  by  making  it  the  negative  elec- 
trode of  a  small  Bunsen's  battery  consisting  of  two  cells,  each  of 
half  a  litre  in  capacity.    The  positive  electrode  was  a  thick  pla- 
tinum wire  placed  side  by  side  with  the  palladium  wire,  and  ex- 
tending the  whole  length  of  the  latter,  within  a  tall  jar  filled  with 
dilute  sulphuric  acid.    The  palladium  wire  had,  in  consequence, 
hydrogen  carried  to  the  surface  for  a  period  of  one  and  a  half 
hour.    A  longer  exposure  was  found  not  to  add  senibly  to  the 
charge  of  hydrogen  acquired  by  the  wire.    The  w^ire  was  again 
measured,  and  the  increase  in  length  noted.    Finally,  the  wire 
being  dried  with  a  cloth,  was  divided  at  the  marks,  and  the  charged 
portion  heated  in  a  long  narrow  glass  tube  kept  vacuous  by  a 
Sprengel  aspirator.    The  whole  occluded  hydrogen  was  thus  col- 
leted  and  measured ;  its  volume  is  reduced  by  calculation  to  Bar. 
760  m.m.,  and  Therm.  0°  C. 
The  original  length  of  the  palladium  wire  exposed  was  609444 
m.m.  (23-982  inches),  and  its  weight  1-6832  grm.  The  wire  re- 
ceived a  charge  of  hydrogen  amounting  to  936  times  its  volume, 
measuring  128  c.c,  and  therefore  weighing  0*01147  grm.  When 
the  gas  was  ultimately  expelled^  the  loss  as  ascertained  by  direct 
weighing  was  0  01164  grm.  The  charged  wire  measured  618*923 
m.m.,  showing  an  increase  in  length  of  9*779  m.m.  (0*385  inch). 
The  increase  in  linear  dimensions  is  from  100  to  101*605;  and 
in  cubic  capacity  assuming  the  expansion  to  be  equal  in  all  direc- 
tions, from  100  to  104*908.    Supposing  the  two  metals  united 
