200  '       On  Breakage  of  Glass  Vessels.  {^iyi-J^n"!^' 
placed  the  water  on  the  fire  and  observed  the  thermometer ;  filled  the 
bottle  to  the  next  mark  and  observed  the  thermometer  again.  Con- 
tinued in  the  same  manner  until  the  vessel  was  full,  replacing  the 
water  on  the  fire  each  time  so  as  to  keep  it  constantly  boiling.  The 
results  were  as  follows  : 
At  the  two  ounce  point,  the  mercury  stood  at  130°,  showing  that 
the  first  two  fluid  ounces  of  the  water  had  lost  82  degrees  of  heat  in 
passing  down  the  rod ;  at  the  four  ounce  point  the  mercury  stood  at 
160°,  showing  a  loss  of  52°  ;  at  the  six  ounce  point  it  stood  at  168°,  at 
the  eight  ounce  point  it  stood  at  170°,  at  the  ten,  twelve,  sixteen  and 
twenty  ounce  points  it  stood  at  172°,  175°,  179°  and  181°  respec- 
tively ;  showing  losses  of  42°,  40°,  37°,  33°  and  31°. 
These  experiments  almost  satisfy  me  that  I  am  right  in  the  suppo- 
sition before  expressed,  that  the  effect  is  due  simply  to  the  absorption 
of  heat  from  the  liquid  by  the  rod.  Whether  I  am  correct  or  not 
in  the  explanation  can  make  no  difference  in  regard  to  the  utility  of 
the  process.  Of  course  the  success  of  the  process  depends  almost 
entirely  upon  proper  manipulation.  To  insure  success,  I  recommend 
that  the  rod  be  placed  on  the  centre  of  the  bottom  of  the  vessel,  that 
it  be  held  perpendicularly,  so  as  not  to  touch  any  part  of  the  side  or 
lip,  that  it  be  of  such  length  as  to  project  six  inches  above  the  top  of 
the  bottle,  that  the  lip  of  the  pouring  vessel  be  placed  against  the  rod, 
and  that  the  liquid  be  poured  slowly  so  that  none  of  it  may  leave  the 
rod  until  it  reaches  the  bottom.  Rods  of  about  the  thickness  of  J  of 
an  inch  will  be  found  most  convenient.  When  a  funnel  is  used,  the 
rod  cannot  be  placed  perpendicularly,  but  may  be  so  placed  that 
the  point  of  the  funnel  rests  against  the  rod.  As  to  the  material  of 
which  the  rods  are  made,  it  seems  to  make  very  little  difference ;  I 
have  generally  used  rods  of  iron,  as  that  metal  is  least  liable  to  con- 
taminate medicinal  substances.  Rods  of  copper  or  brass  will  answer, 
and  for  liquids  containing  tannin  are  to  be  preferred.  If  I  am 
correct  in  my  explanation,  it  will  naturally  follow  that  rods  which 
are  the  best  absorbers  will  be  most  efficient ;  and  consequently  that 
rods  made  of  rough  iron  will  be  the  best.  The  idea  of  using  rods  of 
glass  never  entered  my  mind  until  lately,  when  I  performed  the 
eleventh  and  twelfth  experiments.  The  glass  rods  answered  in  these 
cases,  and  for  liquids  which  would  be  injured  by  contact  with  metals 
are  to  be  preferred,  but  must  be  used  with  great  care  on  account  of 
their  inferior  absorbing  power. 
