POWEE  OF  METALS  AND  ALLOTS  TO  CONDUCT  HEAT. 
357 
We  also  thought  that  it  would  be  interesting  to  ascertain  what  would  be  the  influence 
of  another  non-metallic  substance  on  a metal,  and  we  accordingly  made  the  following 
series : — 
Found. 
Mean. 
Conductibility. 
Silver=  1000. 
Cast  copper  
25-87 
18-20 
811 
Copper  with  1 per  cent,  of  arsenic  ... 
fl8-l  1 
[18-3  J 
570 
Copper  with  0'5  per  cent,  of  arsenic 
21-3 
[21-4  j 
21-35 
669 
Copper  with  0‘25  per  cent,  of  arsenic 
i 
[24-7 
24-5  J 
24-60 
771 
These  results  confirm  the  influence  of  a non-metallic  body  on  the  conductibility  of  a 
metal.  It  is  interesting  to  observe  that  the  influence  of  arsenic  on  the  conduction  of 
heat  on  copper  is  in  ratio  with  the  increased  quantity  of  arsenic. 
We  have  also  examined  a great  number  of  alloys  with  the  hope  of  throwing  some  light 
on  their  chemical  composition,  and  we  trust  that  the  facts  which  we  are  about  to 
describe  will  not  only  tend  to  illustrate  this  point,  but  wall  also  be  of  interest  from  the 
new  and  various  results  observed. 
We  have  also  made  a great  variety  of  experiments  with  the  view  of  ascertaining  if 
there  be  a general  law  in  connexion  with  the  conduction  of  heat  by  alloys,  and 
although  we  could  not  trace  any  general  rule,  still  we  observed  several  useful  facts. 
The  conduction  of  heat  by  alloys  may  be  considered  under  three  general  heads : — 
1.  Alloys  which  conduct  heat  in  ratio  with  the  relative  equivalents  of  the  metals 
composing  them. 
2.  Alloys  in  which  there  is  an  excess  of  equivalents  of  the  worse  conducting  metal 
over  the  number  of  equivalents  of  the  better  conductor,  such  as  alloys  composed  of 
ICu  and  2Sn ; ICu  and  3Sn ; ICu  and  4Sn,  &c.,  and  which  present  the  curious  and 
unexpected  rule  that  they  conduct  heat  as  if  they  did  not  contain  a particle  of  the 
better  conductor ; the  conducting  power  of  such  alloys  being  the  same  as  if  the  square 
bar  which  we  were  examining  was  entirely  composed  of  the  worse  conducting  metal. 
A not  less  remarkable  fact  is  that  the  alloys  of  a series  such  as  those  of  2 equivalents 
of  bismuth  and  1 of  lead,  3Bi  and  IPb,  4Bi  and  IPb,  5Bi  and  IPb,  all  conduct  the 
same,  \iz.  about  1'9,  the  various  increasing  quantities  of  lead  exercising  no  influence  on 
the  conductibility  of  the  alloys.  The  results  obtained  with  this  class  of  alloys  are  most 
important  to  engineers ; for  it  will  be  seen  in  the  case  of  the  alloys  of  brass  and  bronze, 
that  no  increase  is  gained  in  the  conductibility  of  an  alloy  by  increasing  the  quantity  of 
a good  conductor ; nay,  in  many  cases  it  would  be  a decided  loss,  unless  a sufficient 
quantity  of  the  better  conducting  metal  be  employed  to  bring  the  alloy  under  the  third 
head. 
3.  Alloys  composed  of  the  same  metals  as  the  last  class,  but  in  which  the  number  of 
equivalents  of  the  better  conducting  metal  is  greater  than  the  number  of  equivalents  of 
