POAVEE  OF  IVIETALS  AND  ALLOYS  TO  CONDUCT  HEAT. 
351 
perforated  with  two  holes ; the  vessels  are  covered  with  wadding,  and  the  lid  of  the  box 
shut.  Through  one  of  the  holes  in  the  vessel  C is  introduced  a very  sensitive  thermo- 
meter, graduated  in  tenths  of  a degree ; in  the  other  hole  is  a small  whalebone  rod,  E, 
having  at  its  extremity  a piece  of  vulcanized  rubber  to  agitate  thoroughly  the  water  in 
the  vessel  during  the  experiment,  and  render  it  of  a uniform  temperature.  When  the 
water  in  the  vessel  C has  attained  a fixed  temperature  (which  is  generally  within  one 
degree  of  that  of  the  room),  a thermometer  is  introduced  into  the  vessel  B,  and  200 
cub.  cent,  of  boiling  water  poured  in  by  means  of  a funnel,  which  communicates  with  a 
tube  F ; the  temperature  of  the  liquid  falls  to  86°  or  88°,  but  is  again  raised  within  three 
minutes  to  90°,  by  a small  jet  of  steam,  generated  in  a fiask,  the  water  in  which  is 
kept  boiling  during  the  whole  of  the  experiment.  A few  experiments  soon  enable  the 
operator  to  keep  up  a constant  temperature  of  90°  in  the  vessel  B during  the  quarter 
of  an  hour  which  the  experiment  requires.  Immediately  on  the  boiling  water  being 
poured  into  the  vessel  B,  the  operator  looks  attentively  at  the  scale  of  the  thermometer 
in  vessel  C,  and  as  soon  as  he  perceives  the  column  of  mercury  rising,  he  carefully  marks 
the  second  and  minute  dials  of  his  watch,  and  makes  similar  marks  fifteen  minutes 
further  on.  During  this  time  the  operator  agitates  the  liquid  in  vessel  C with  the 
agitator  E,  and  every  five  minutes  marks  down  the  rise  of  temperature.  The  water  in 
the  vessel  B has  a uniform  temperature,  owing  to  the  agitation  produced  in  it  by  the 
small  jet  of  steam  which  arrives  almost  close  to  the  bottom. 
The  following  figures  will  show  how  insignificant  was  the  radiation  from  the  large 
vessel  B,  containing  200  cub.  cent,  of  water  at  90°  C.,  to  the  smaller  vessel  C,  contain- 
ing 50  cub.  cent,  of  water  at,  natural  temperature,  when  the  two  vessels  were  not  con- 
nected by  a metallic  bar,  though  placed  in  their  usual  position  in  the  apparatus,  for  in 
fifteen  minutes  the  temperature  of  the  water  in  the  smaller  vessel  C only  increased  0-05 
of  a degree,  and  in  half  an  hour  only  0°-7. 
Temperature  of  the  water 
in  the  vessel  C. 
17-20 
After  15  minutes 
17-25 
After  30  minutes 
17-90 
Therefore  the  entire  increase  of  temperature  in  the  vessel  C,  in  our  experiment,  must 
have  been  due  to  tlie  heat  conducted  by  the  bar. 
It  was  found  that  it  required  twenty-four  hours  before  the  temperature  of  the  water 
in  the  vessels  of  the  apparatus  was  in  equilibrium  with  that  of  the  surrounding  atmo- 
sphere, when  200  cub.  cent,  of  boiling  water  was  poured  into  the  vessel  B,  and  the 
apparatus  left  to  cool.  It  might  be  objected  that  in  our  experiments  we  neglected  to  * 
take  into  account  the  heat  absorbed  by  the  sides  of  the  vessel  C ; but  we  found,  from 
a great  number  of  experiments,  that  whether  we  took  into  consideration,  or  not,  the 
amount  of  heat  absorbed,  it  did  not  afiect  in  any  degree  the  relative  conductibility  of 
the  metals  and  their  alloys ; but  it  must  be  borne  in  mind  that  it  was  not  the  absolute 
MDCCCLVIII.  3 B 
