RELATION  OF  HYDROGEN  TO  PALLADIUM. 
177 
proportion  of  from  ten  to  twenty  minims  of  ether  purus,  P.  B., 
to  two  drachms  of  oil. '  One  advantage  of  the  combination  seems 
to  be  the  power  of  the  former  to  mask  the  unpleasant  properties 
of  the  latter.  Dr.  Foster  recites  many  cases  to  prove  that  where 
cod-liver  oil  by  itself  had  failed  to  produce  improvement  and  to 
arrest  the  wasting,  the  addition  of  ether  has  been  eminently  suc- 
cessful in  allaying  nausea,  and  producing  a  decided  increase  in 
the  weight  of  the  patient. — Lond.  Pharm.  Journ.^  Jan.^  1869. 
ON  THE  RELATION  OF  HYDROGEN  TO  PALLADIUM.* 
By  Thomas  Graham,  P.  R.  S.,  Master  of  the  Mint. 
It  has  often  been  maintained  on  chemical  grounds  that  hydro- 
gen gas  is  the  vapor  of  a  highly  volatile  metal.  The  idea  forces 
itself  upon  the  mind  that  palladium  with  its  occluded  hydrogen 
is  simply  an  alloy  of  this  volatile  metal  in  which  the  volatility  of 
the  one  element  is  restrained  by  its  union  with  the  other,  and 
which  owes  its  metallic  aspect  equally  to  both  constituents.  How 
such  a  view  is  borne  out  by  the  properties  of  the  compound  sub- 
stance in  question  will  appear  by  the  following  examination  of 
the  properties  of  what,  assuming  its  metallic  character,  would 
fairly  be  named  hydrogenium. 
Density. — The  density  of  palladium  when  charged  with  800  to 
900  times  its  volume  of  hydrogen  gas  is  perceptibly  lowered,  but 
the  change  cannot  be  measured  accurately  by  the  ordinary  method 
of  immersion  in  water,  owing  to  a  continuous  evolution  of  minute 
hydrogen  bubbles  which  appear  to  be  determined  by  contact  with 
the  liquid.  However,  the  linear  dimensions  of  the  charged  pal- 
ladium are  altered  so  considerably  that  the  difference  admits  of 
an  easy  measurement,  and  furnishes  the  required  density  by  cir- 
culation. Palladium  in  the  form  of  wire  is  readily  charged  with 
hydrogen  by  evolving  that  gas  upon  the  surface  of  the  metal  in 
a  galvanometer  containing  dilute  sulphuric  acid,  as  usual.*  The 
length  of  the  wire  before  and  after  a  charge  is  found  by  stretch- 
ing it  on  both  occasions,  by  the  same  moderate  weight,  such  as 
will  not  produce  permanent  distention,  over  the  surface  of  a  flat 
graduated  measure.  The  measure  was  graduated  to  hundredths 
of  an  inch,  and  by  means  of  a  vernier  the  divisions  could  be  read 
*  Proceed.  Royal  Society,  p.  422,  1868. 
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