350 
ME.  CEACE  CAEVEET  AET)  j\IE.  E.  JOHXSOiS'  OX  THE  EELATITE 
amalgams,  cominced  that  if  the  chemical  nature  of  alloys  and  amalgams  is  still  enve- 
loped in  darkness,  it  is  because  they  have  been  prepared  with  impure  or  commercial 
metals,  and  not  made  in  equivalent  quantities.  The  consequence  has  been,  that  as 
metals  have  only  a slight  affinity  for  each  other,  and  as  the  definite  compounds  which 
they  have  a tendency  to  form  were  mixed  with  an  excess  of  one  of  the  metals  employed, 
the  alloys  produced  have  presented  properties  which  could  lead  to  no  infonnation  as  to 
their  nature.  These  difficulties  have  been  increased  by  the  fact,  that  in  many  alloys, 
such  as  those  of  copper  and  tin,  or  copper  and  zinc,  the  metals  have  a tendency,  when 
allowed  to  cool  slowly,  to  form  several  crystallizable  compounds,  difiFering  in  their  com- 
position in  the  various  parts  of  the  alloys ; the  less  fusible  being  on  the  exterior,  and 
those  more  so  in  the  interior  of  the  mass.  The  impmities  existing  in  commercial  metals 
are  often  so  large  as  considerably  to  modify  the  properties  of  their  alloys ; for  we  have 
found  in  our  researches  that  if  1 per  cent,  of  a metal  be  added  to  99  of  another,  it  alters 
its  conducting  power  most  materially.  To  avoid  these  causes  of  error,  we  have  composed 
our  alloys  of  pure  metals  and  employed  definite  proportions. 
The  apparatus  which  we  used  is  composed  of  a deal  box  (Plate  XXVII.),  A,  105 
millims.  in  width,  165  millims.  in  length,  and  220  millims.  in  height ; with  a cover,  and 
painted  white  externally  and  internally.  Inside  this  box  are  two  'siilcanized  india- 
rubber  square  vessels,  the  sides  of  which  are  15  millims.  thick.  The  larger  vessel,  B, 
measures  internally  52  millims.  on  the  side  and  125  millims.  deep,  and  is  capable  of 
containing  336  cub.  cent,  of  water.  The  smaller  vessel,  C,  is  27  millims.  on  the  side 
and  125  millims.  deep,  and  has  a capacity  of  90  cub.  cent. 
These  vessels  are  painted  white  and  surrounded  with  wadding;  and  stdl  fui'ther  to 
prevent  any  radiation  of  heat,  a deal  board,  D,  is  placed  between  the  two  vessels.  So 
little  heat  is  radiated  from  the  vessel  B,  when  it  contains  200  cub.  cent,  of  water  at  90°, 
to  the  smaller  vessel  C,  containing  50  cub.  cent,  at  16°,  that  in  a quarter  of  an  hour, 
the  time  required  for  our  experiments,  the  water  in  the  latter  vessel  did  not  rise  one- 
tenth  of  a degree  Centigrade.  Therefore  all  sensible  radiation  and  conduction  was 
avoided,  and  the  rise  of  temperature  in  this  vessel,  during  the  experiment,  must  have 
been  enthely  due  to  the  heat  conducted  by  the  square  bar  of  metal  (G)  used.  This  bar 
is  6 centims.  long  and  1 centim.  square,  and  is  so  arranged  in  the  experiment,  that 
1 cub.  cent,  is  in  the  vessel  B,  1 cub.  cent,  in  the  vessel  C ; 3 cub.  cent,  are  covered 
by  the  sides  of  the  boxes  through  which  it  passes ; and  the  last  1 cub.  cent.,  mai'ked  H, 
is  covered  with  a piece  of  vulcanized  india-rubber  tubing,  and  the  whole  made  secme 
from  any  leakage  by  lining  the  sides  of  the  holes,  through  which  the  bar  passes,  with  a 
varnish  made  of  caoutchouc  dissolved  in  benzine.  This  bar  is  placed  54  millims.  fi-om 
the  bottom  of  B,  and  12  milhms.  from  the  bottom  of  C. 
When  we  desire  to  make  an  experiment,  the  vessels  are  put  in  water  so  as  to  equalize 
their  temperature ; they  are  then  carefully  wiped  and  placed  m the  wooden  box,  sin- 
rounded  with  wadding,  and  50  cub.  cent,  of  water,  at  the  temperatm’e  of  the  room,  poined 
into  the  vessel  C ; the  two  boxes  are  then  covered  with  vulcanized  india-rubber  lids,  each 
