POWEE  OF  METALS  AND  ALLOTS  TO  CONDUCT  HEAT. 
356 
sent  their  exact  conducting  power,  but  they  are  at  all  events  very  near  the  truth.  We 
endeavom-ed  to  ascertain  the  conducting  power  of  potassium  in  the  same  way,  but  failed, 
owing  to  the  tendency  which  potassium  has  to  granulate  when  melted  under  benzine. 
We  think  it  our  duty  to  state,  that  we  are  aware  of  the  respective  works  of  M.  Lang- 
BERG  and  of  MM.  Wiedemaxx  and  Franz,  but  that  we  have  not  followed  their  thermo- 
electrical process,  as  we  deemed  our  method  capable  of  giving  more  direct  and  reliable 
results.  We  have,  however,  great  pleasure  in  confirming  their  results  with  reference  to 
the  superior  conducting  power  of  silver  to  that  of  gold,  though  the  order  of  conducti- 
bility  of  the  other  metals  as  determined  by  our  process  is  different  from  theirs. 
In  determining  the  conducting  power  of  metals  great  attention  must  be  paid  to  their 
physical  state,  as  their  conductibility  is  modified  by  their  molecular  condition. 
Influence  of  Molecular  Condition. 
We  found  that  the  conducting  power  of  several  metals  was  different  when  they  were 
roUed  out  into  bars,  or  when  cast.  Thus,  for  example, — 
Conductibility  found.  Conductibility.  Silver  =1000. 
Rolled  copper  . . . 26'95  845 
Cast  copper . . . . 25‘87  811. 
It  is  probable  that  the  reason  why  rolled  metal  conducts  heat  better  than  the  same 
metal  when  simply  cast,  is  that  the  molecules  composing  the  rolled  metal  are  in  closer 
contact  than  those  composing  the  cast  metal,  owing  to  the  process  of  rolling ; and  it  is 
worthy  of  observation,  that  this  view  agrees  with  Mr.  J.  P.  Joule’s  theory,  that  heat 
travels  in  bodies  by  the  vibration  of  matter,  and  not  by  the  fluid  called  caloric,  travelling 
between  the  interstices  of  the  molecules. 
Influence  of  Crystallization. 
The  influence  of  the  molecular  arrangement  is  clearly  illustrated  in  the  following- 
examples,  where  it  is  seen  that  the  conducting  power  of  zinc,  antimony,  and  bismuth 
is  modified  according  to  the  axes  of  crystallization.  Thus  the  conducting  power  of  zinc 
is  different  if  the  sample  for  experiment  is  cast  horizontally  or  vertically ; for  example, 
Conductibility  found.  Conductibility.  Silver  =1000. 
Zinc  cast  vertically  ..  20-03  628 
Zinc  cast  horizontally  . 19-40  608 
If  these  two  square  bars  be  broken  and  examined,  they  present  a very  great  difference. 
The  one  cast  vertically  has  four  axes  of  crystallization,  all  starting  from  the  centre 
and  proceeding  towards  each  angle  of  the  bar,  as  shown  in  Plate  XXVII.  The  one 
cast  horizontally  has  one  centre  line  or  axis  of  crystallization,  which  divides  the  square 
bar  into  three  parts. 
The  results  obtained  with  antimony  are  the  following : — 
Conductibility  found.  Conductibility.  Silver =1000. 
Antimony  cast  vertically  . . 6-12  192 
Antimony  cast  horizontally  . 6-85  215 
