208    On  the  Action  of  Nuclei  on  a  Supersaturated  Solution. 
rises  to  the  surface  in  bubbles.  In  this  way  ten  or  twelve  bub- 
bles of  air  may  form  a  ring  on  the  surface  in  contact  with  the 
glass.  If  a  small  flame  of  a  spirit-lamp  be  now  applied  to  the 
bottom  of  the  tube,  a  bubble  of  steam  will  often  ascend  through 
the  oil  and  fish  down  one  or  two  or  three  of  these  bubbles,  which 
may  burst  and  scatter  a  multitude  of  minute  bubbles  against  the 
side  of  the  tube,  where  they  remain  a  long  time.  It  would  be 
quite  natural  to  suppose  that  these  bubbles  are  derived  from  the 
water  instead  of  from  the  superincumbent  air.  It  is  curious  to 
see  how  easily  a  bubble  of  steam  adheres  to  a  bubble  of  air.  I 
believe  this  to  be  the  source  of  the  air  found  in  boiling  liquids 
in  the  form  in  which  this  experiment  is  arranged. 
In  conclusion,  I  will  give  the  results  of  a  few  experiments 
which  were  made  after  reading  M.  Solaro's  paper. 
Exp.  1.  Distilled  water  was  poured  into  a  clean  flask,  and 
this  was  placed  over  the  flame  of  a  spirit-lamp.  Two  vortices  of 
steam-bubbles  continued  to  ascend  from  two  small  but  visible 
black  specks  in  the  bottom  of  the  flask  so  long  as  the  boiling 
was  continued. 
Exp.  2.  A  rat's-tail  file  placed  in  boiling  water  gave  off  steam 
from  every  part  of  the  immersed  surface.  The  file  was  washed 
in  soap  and  water.  It  was  now  active  at  several  points.  It 
was  then  washed  in  alcohol,  it  was  still  active,  and  on  closely 
examining  these  points  they  were  evidently  rust.  The  file  was 
put  into  dilute  sulphuric  acid  and  dried  in  hot  air.  It  was  then 
inactive.  Now  let  me  ask  why  the  file,  after  the  first  cleaning, 
should  act  in  one  or  two  points  only,  and  not  over  its  whole 
surface,  if,  according  to  the  theory,  rough  bodies  are  most  effec- 
tive in  carrying  down  air  ? 
Exp.  3.  Drew  the  file  through  the  hand  that  had  been 
lightly  smeared  with  oil.  The  file  when  introduced  into  the  hot 
water  was  immediately  covered  with  bubbles,  and  bubbles  escaped 
from  its  surface  during  several  minutes,  so  long  as  the  water  was 
just  about  the  boiling-point. 
Exp.  4.  A  clean  glass  rod  put  into  boiling  water  was  entirely 
free  from  bubbles.  It  was  then  covered  with  a  film  of  castor- 
oil,  and  when  restored  to  the  boiling  water  became  immediately 
covered  with  small  bubbles,  while  large  bubbles  escaped  from 
various  parts  of  its  surface. 
Exp.  5.  Wood-spirit,  boiling  at  140°  F.,  contained  in  a  test- 
tube,  was  plunged  into  a  flask  of  hot  water.  A  clean  glass  rod 
that  had  been  exposed  during  an  hour  to  the  air  of  my  garden 
was  inactive.  It  was  drawn  through  the  hand  that  had  been 
made  slightly  greasy  with  lard,  and  when  reinserted  it  produced 
such  a  burst  of  vapour  as  to  turn  out  half  the  contents  of  the  tube. 
A  similar  result  was  produced  with  ether  and  bisulphideof  carbon. 
Highgate  N.,  February  12, 1872. 
