206  Mr.  C.  Tomlinson  on  the  Action  of  Nuclei  in  separating 
face  so  long  as  it  continues  to  be  covered,  more  or  less,  with  a 
film  of  a  body  that  can  be  touched  by  air  or  vapour  and  not  by 
water.  A  flint  pebble  that  has  been  exposed  to  the  air  of  a  room 
or  handled,  and  put  into  a  solution  of  gas  or  of  vapour,  imme- 
diately becomes  covered  with  bubbles ;  but  if  broken  in  half  and 
returned  to  the  solution,  not  a  single  bubble  is  to  be  seen  on 
the  fractured  parts ;  for  these  are  specimens  of  nature's  clean 
surfaces.  If  air  has  any  function  to  perform  in  the  matter,  why 
should  the  unclean,  and  not  the  clean  surfaces  carry  it  down  ? 
Some  liquids  contain  their  own  nuclei,  as  in  the  case  of  milk. 
When  this  is  heated  over  the  fire,  it  becomes  more  and  more 
charged  with  vapour ;  and  at  a  certain  point,  the  particles  of  but- 
ter disseminated  through  it,  assisting  the  expansive  force  of  the 
heat,  produce  such  a  sudden  t&rst  of  vapour  as  to  cause  the 
liquid  to  boil  over. 
If  a  body,  such  as  a  glass  rod,  be  made  chemically  clean,  and 
then  be  plunged  into  a  supersaturated  solution  of  gas  or  of  va- 
pour, not  a  single  bubble  will  be  seen  upon  it,  because  both 
water  and  gas,  or  water  and  vapour,  adhere  to  it  with  equal  force. 
If  the  clean,  but  wet,  glass  rod  be  left  to  dry  in  the  dusty  air  of 
the  room,  and  when  dry  be  plunged  into  the  solution,  it  will  be 
active ;  but  if  left  to  dry  in  the  pure  outer  air  of  the  country, 
and  when  dry  be  plunged  into  the  solution,  it  is  inactive,  because 
it  is  still  in  a  •  clean  or  catharized  state.  The  same  remark 
applies  to  a  supersaturated  saline  solution. 
I  find  it  difficult  to  reply  to  such  objections  as  those  that  M. 
Solaro  has  brought  forward,  because,  apparently  without  repeat- 
ing my  experiments,  he  sometimes  refuses  to  accept  my  account 
of  them  as  true.  For  example,  he  cannot  understand  how  a  cage 
of  fine  wire  gauze  can  be  introduced  into  a  liquid  at  or  near  the 
boiling-point  and  still  retain  some  of  its  air.  "  La  cage  etait 
descendue  doucement  dans  l'eau,  et,  par  consequent,  h,  mesure 
que  sa  partie  inferieure  descendait,  Fair  devait  sortir  doucement 
aussi  par  la  partie  superieure."  If,  instead  of  making  this  re- 
mark, M.  Solaro  had  simply  tried  the  experiment,  he  would  not 
have  placed  himself  in  the  position  of  the  man  who,  being  told 
that  the  facts  were  against  him,  replied,  "  So  much  the  worse 
for  the  facts  !  " 
Again,  when  I  produce  ebullition  by  the  contact  of  an  unclean 
body  with  a  liquid  near  its  boiling-point,  M.  Solaro  says  "  Pebul- 
lition  arriverait  sans  le  contact  quelques  instants  plus  tard." 
Now  that  is  just  the  very  thing  that  it  would  not  do;  for  I  ar- 
ranged the  hot-water  bath  so  as  to  keep  the  liquid  to  be  operated 
on  near  to,  but  not  at  the  boiling-point. 
Once  more,  I  say  that  the  glass  vessels  in  which  liquids  are 
usually  boiled  and  distilled  by  the  chemist,  are  frequently  dotted 
