Electrically  Prepared  Colloidal  Solutions. 
Table  II. 
439 
Metal 
in 
Sol. 
Used  for  sparking 
in  preparation. 
Specific 
Conductivity 
of  Sol. 
Sign  of 
Charge 
on 
Particles. 
Velocity  in 
cms.  per  sec. 
per  volt  per  cm. 
Voltage. 
Current. 
Platinum   ... 
Gold  
Silver       ..... 
40  t. 
50  t. 
60  v. 
30  v. 
30  v. 
50  v. 
7 "5  amp. 
7-5     .. 
7-5     „ 
6-5     „ 
6-5     „ 
6-5    „ 
21-3x10-6 
105x10-6 
19-0x10-6 
70x10-6 
15-0x10-6 
9-4x10-6 
4- 
+ 
+ 
20-3  XlO~5 
2 1-6  X  10 -5 
236  Xl0"5 
11-OxlO-5 
12-0  x  10- 5 
19-OxlO-5 
Bismuth 
Lead  
As  has  been  mentioned  above,  the  first  three  solutions  of 
Table  II.  are  extremely  stable,  the  metals  remaining  appa- 
rently uniformly  in  solution  for  months,  while  the  solutions 
of  bismuth,  lead,  and  iron  would  be  precipitated  in  the 
course  of  a  week  or  so.  The  bismuth  solution  is  dark  brown 
in  colour,  not  unlike  the  silver  solution  in  appearance,  The 
lead  solution  is  initially  dark  brown  as  well,  but  if  left  in 
contact  with  the  air  the  particles  rapidly  turn  white,  doubt- 
less on  account  of  the  formation  of  a  carbonate  ;  but  whether 
in  the  brown  or  white  state,  the  particles  move  to  the  negative 
electrode  in  an  electric  field.  The  iron  solution  always 
possesses  a  reddish-brown  colour,  which  points  to  formation 
of  a  hydroxide;  this  quite  agrees  with  the  fact  given  bv 
Linder  and  Picton  that  in  chemically  prepared  colloidal 
solutions  of  ferric  hydrate  the  particles  move  towards  the 
negative  electrode. 
If  there  are  particles  of  varying  sizes  present  in  any  one 
solution,  no  indication  of  any  difference  in  velocity  of  the 
various  particles  was  evident ;  however,  this  does  not  justify  the 
assumption  that  the  particles  are  all  of  the  same  size,  because, 
according  to  the  theory  given  by  Lamb,  the  velocityof  similarly 
constituted  particles  is  independent  of  the  size  and  shape.  If 
particles  of  different  sizes  do  exist  in  these  electrically  prepared 
solutions  the  size  would  probably  depend  on  the  violence  of  the 
sparking  during  the  preparation  of  the  solution.  Three  silver 
solutions  were  prepared,  using-  varying  currents  and  voltages 
for  producing  the  spark,  all  other  conditions  being  the  same 
except  the  time  of  sparking.  As  shown  in  Table  111.,  the 
differences  in  the  velocities,  which  were  all  determined  at 
11°  0.,  are  all  within  the  limits  of  error  in  the  experime   i 
