524 
ON  DROPS. 
L  L  L,  when  from  a  liquid  a  liquid  drops  through  a  liquid. 
Of  these  three  cases  the  first  and  last  may  be  reversed, — as 
when  from  a  solid  a  liquid  ascends  through  a  liquid  ;  and  when 
from  a  liquid  a  liquid  ascends  through  a  liquid.  The  middle 
case,  of  course,  cannot  be  reversed  as  it  would  presuppose  the 
existence  of  a  liquid  lighter  than  a  gas. 
The  case  8  L  G  is  the  most  common  and  important,  and  is 
the  only  one  at  present  investigated  by  Professor  Guthrie.  In 
this  case  the  variable  conditions  are  the  self-attraction  and  co- 
hesion of  the  liquid,  which  is  dependent  on  its  chemical  and 
physical  constitution ;  the  adhesion  between  the  solid  and  the 
liquid,  which  is  dependent  on  their  relative  chemical  and  physi- 
cal constitution,  and  the  shape  of  the  solid.  Temperature  has 
also  a  considerable  effect  on  the  solid  liquid  and  gas.  There  are 
also  two  other  conditions, — the  adhesion  of  the  gas  to  the  solid 
and  to  the  liquid  ;  but  as  atmospheric  air  at  ordinary  barometric 
pressure  is  always  the  gaseous  medium  through  which  the  drop 
falls,  these  need  not  be  noticed.  The  condition,  however,  which 
has  the  greatest  effect  on  the  size  of  the  drop  is  the  interval 
which  takes  place  between  the  successive  drops,  and  called  by 
Professor  Guthrie  the  growth-time.  Ceteris  paribus,  therefore 
we  may  say  that  the  growth-time  being  constant,  the  size  of  the 
drops  produced  will  be  the  same  for  the  same  liquid. 
In  the  first  series  of  experiments  Professor  Guthrie  used  an 
ivory  sphere  having  a  diameter  of  22*1  millimetres,  and  sus- 
pended from  a  retort  stand  by  three  fine  wires.  The  sphere 
was  dipped  in  hydrochloric  acid  so  as  to  deaden  its  surface. 
The  liquid  under  experiment  was  contained  in  a  cylindrical 
vessel,  and  always  kept  at  the  same  level  by  means  of  a  pear- 
shaped  reservoir,  containing  the  same  liquid,  suspended  over  it 
with  the  mouth  just  touching  the  surface.  The  liquid  was  con- 
veyed to  the  ivory  ball,  the  upper  half  of  which  was  covered 
with  cotton  wool,  by  a  syphon  which  could  be  easily  raised  or 
lowered  at  pleasure,  so  as  to  regulate  exactly  the  amount  of 
liquid  flowing  on  to  the  ball.  The  end  of  the  syphon  was 
slightly  turned  up,  and  touched  a  plug  of  cotton  on  the  top  of 
the  sphere.  The  drops  formed  were  received  in  a  funnel  placed 
in  a  beaker. 
Cocoa-nut  oil  was  the  liquid  used  in  the  first  series  of  experi- 
