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XVIII.  On  the  Relative  Power  of  Metals  and  Alloys  to  conduct  Heat. — Part  I.  By 
F.  Ckace  Calveet,  Esq.,  F.C.S.,  Corr.  Mem.  Roy.  Acad.  Turin,  Societe  de  Pharnmcie, 
Paris,  &c.;  and  Kichaed  Johnson,  Esq.,  F.C.S.,  &c.  Commumicated  by  Professor 
Stokes,  Sec.  R.S. 
Eeceived  February  19, — Eead  March  25,  1858. 
Metals  and  their  aUoys  being  now  so  extensively  employed  in  arts  and  manufactures, 
and  for  instruments  of  precision,  we  have  thought  that  it  would  be  interesting,  in  a 
scientific  or  commercial  point  of  view,  if  we  were  to  examine  their  conductibility  care- 
fiiUy  and  completely. 
To  enable  us  to  determine  with  accm-acy  the  conducting  power  of  all  the  ordinary 
metals,  and  of  seventy  of  their  alloys  and  thhty  of  their  amalgams,  we  had  to  find  out  a 
new  method  of  determining  the  conducting  power  of  metals ; for  the  process  followed  by 
M.  Despeetz  could  only  give  results  to  be  relied  upon  for  a few  of  the  best  conductors, 
such  as  silver,  gold,  and  copper.  Further,  his  process,  which  consists  in  having  a long 
and  thick  bar  of  metal,  so  as  to  allow  holes  to  be  diiUed,  in  which  mercury  and  the  bulb 
of  a thermometer  are  inserted,  would  have  required  a large  quantity  of  each  metal  in  a 
state  of  purity,  the  labom’  of  obtaining  which,  even  comparatively  pure,  is  well  known. 
Also  fi’om  the  fact  of  mercuiy  being  employed,  we  should  have  been  unable  to  ascertain 
the  conducting  power  of  such  important  alloys  as  brass  and  bronzes,  and  could  not 
have  applied  the  process  to  amalgams. 
The  method  which  we  have  followed  gives  such  consistent  results,  that  we  have  not 
only  been  able  to  determine  the  influence  exercised  on  the  conducting  power  of  metals 
by  the  addition  of  I or  2 per  cent,  of  another  metal,  but  also  to  appreciate  the  difference 
of  conductibility  of  two  alloys  made  of  the  same  metals,  and  only  differing  by  a few  per 
cent,  in  the  relative  proportions  of  the  metals  composing  them.  At  the  same  time  the 
conditions  theoretically  required  in  order  to  obtain  results  independent  of  everything 
but  the  nature  of  the  substances,  are  not  very  rigorously  fulfilled,  so  that  the  term  con- 
ducting power,  as  used  by  us,  must  be  understood  in  a somewhat  qualified  sense,  and  as 
ha\ing  relation  to  our  method  of  determining  it.  We  believe,  however,  that  the  ratios 
of  the  conducting  powers,  as  determined  by  our  method,  do  not  differ  from  those  of  the 
real  conducting  powers. 
Before  describing  the  process  followed  and  examining  the  results  obtained,  it  is  neces- 
sary to  state  that  we  have  made  a great  number  of  experiments  with  the  hope  of  solving 
the  important  chemical  question.  Are  alloys  simple  mixtures  of  metals,  or  are  they  defi- 
nite compounds'?  With  this  view  we  have  operated  on  a large  number  of  alloys  and 
