426 
Mr.  E.  F.  Burton  on  the  Properties  of 
were  in  every  case  found  to  be  negatively  charged,  suggested 
that  they  become  so  electrified  by  the  emission  o£  an  excess 
of  positively  charged  particles,  as  in  the  case  of  metals 
referred  to  above. 
The  experiments  detailed  in  the  present  paper  were  carried 
out  in  order  to  give  some  indication  as  to  how  the  particles 
in  such  solutions  come  to  be  charged.  To  this  end  colloidal 
solutions,  or  sols,  of  many  different  metals  were  formed  in 
water  and  other  liquids,  and  attempts  made  to  determine  the 
charge  on  each  particle  from  the  velocity  with  which  they 
move  in  a  known  electric  field  and  the  size  of  the  particles. 
The  results  of  these  measurements  seem  to  preclude  the  idea 
that  the  charges  arise  from  merely  an  emission  of  charged 
ions  from  the  particles.  A  co-ordination  of  the  results  ob- 
tained with  different  liquid  media  indicates  that  the  formation 
of  colloidal  solutions  is  due  to  a  chemical  reaction  between 
the  metal  and  the  solvent. 
II.  Preparation  of  Solutions  in  Water. 
The  method  of  preparing  the  solutions  was  similar  to  that 
described  by  Bredig  in  the  paper  referred  to  above.  The 
terminals  (B,  fig.  1)  of  a  storage-battery  capable  of  pro- 
viding any  required  voltage  up  to  110  volts,  were  connected 
Fisr.  1. 
through  a  variable  liquid  resistance  (R)  and  ammeter  (A)  to 
two  electrodes  (E1?  E2)  of  the  metal  of  which  a  sol  was 
required.  The  voltage  and  current  used  depended  on  the 
metal  of  which  the  electrodes  consisted ;  such  details  will  be 
found  in  the  tables  given.  The  electrodes  were  held  with 
their  free  ends  beneath  the  surface  of  pure  water  contained 
in  a  clean  porcelain  evaporating-dish  (D)  of  about  100  c.cs. 
capacity,  and  the  current  was  allowed  to  spark  between  them. 
