POWEE  OP  METALS  AND  ALLOYS  TO  CONDUCT  HEAT. 
367 
It  is  probable  that  Cu  2Zn  and  Cu  3Zn  are  definite  compounds,  for  not  only  have  they 
a special  conducting  power  of  their  own  far  below  that  of  the  metals  composing  them, 
but  also  they  are  perfectly  crystallized.  The  most  splendid  of  all  the  brass  alloys  is  the 
alloy  CuZn,  which  is  of  a beautiful  gold  colour  and  crystallizes  in  prisms,  often  3 centims. 
long.  These  crystals  are  also  interesting  on  account  of  their  extraordinary  elasticity. 
It  is  surprising  that  so  cheap  an  alloy  has  not  been  employed  in  commerce,  for  no  com- 
mercial brass  contains  more  than  30  to  35  per  cent,  of  zinc,  whilst  the  above  one  con- 
tains 50’68  of  this  metal.  The  only  explanation  that  we  can  give  of  this  fact  is,  that 
if  copper  be  alloyed  with  more  than  50  per  cent,  of  zinc,  the  alloys  formed  do  not 
possess  the  colour  of  brass,  but  become  white  as  zinc,  and  therefore  the  manufacturers 
have  never  tried  to  unite  these  metals  in  the  exact  proportions  given  above.  We  say 
exact,  for  it  is  remarkable  that  a variation  of  a few  per  cent,  in  the  relative  proportions 
of  the  two  metals  no  longer  yields  the  beautiful  alloy  which  we  have  noticed,  but  only 
a white  and  comparatively  useless  one. 
Alloys  with  excess  of  Copjyer. 
Found. 
Calculated. 
Silver  = 
= 1000. 
Found. 
Calculated. 
Zn  = 
2Cu  = 
33-941 
66-06/ 
19-80 
23-80 
621 
748 
Zn  = 
3Cu= 
25-52  1 
74-48  / 
20-35 
24-37 
638 
764 
Zn  = 
4Cu  = 
20-44  1 
79-56  j 
21-25 
24-67 
666 
770 
Zn  = 
5Cu  = 
17-05  1 
62-95  / 
22-80 
24-87 
715 
780 
We  also  made  a bar  I centim.  cub.  square  of  zinc  and  copper,  placing  a cube  of  each 
metal  alternately,  as  in  No.  3 bar  of  tin  and  copper,  and  the  result  obtained  is  similar ; 
for  we  have — 
Found. 
Calculated. 
Silver  =1000. 
Found. 
Calculated. 
Bar  10 
22-5 
23-33 
705 
731 
The  facts  presented  by  a bar  I centim.  square,  and  composed  of  two  longitudinal  bars 
of  copper  and  zinc,  have  been  described  under  the  bar  No.  5. 
We  also  thought  that  it  might  be  useful  if  we  were  to  analyse  the  following  com- 
mercial alloys,  and  determine  their  respective  conducting  powers. 
3 D 
MDCCCLVIII. 
