﻿and 
  Chemical 
  Reactions 
  in 
  Heterogeneous 
  Systems. 
  54:5 
  

  

  stirring. 
  For 
  this 
  reason 
  I 
  preferred 
  to 
  fix 
  the 
  solid 
  disk, 
  as 
  

   Drucker 
  did, 
  to 
  the 
  stirrer 
  itself, 
  so 
  as 
  to 
  make 
  the 
  number 
  

   of 
  revolutions 
  of 
  the 
  same 
  equal 
  to 
  the 
  number 
  of 
  revolu- 
  

   tions 
  of 
  the 
  stirrer, 
  and 
  I 
  placed 
  the 
  investigated 
  disk, 
  always 
  

   of 
  nearly 
  the 
  same 
  thickness, 
  between 
  the 
  two 
  stirring 
  plates 
  

   of 
  the 
  double 
  stirrer 
  (see 
  PL 
  XYIII. 
  fig. 
  1), 
  so 
  that, 
  besides 
  

   moving 
  the 
  block, 
  the 
  liquid 
  was 
  stirred 
  above 
  and 
  below 
  it. 
  

   The 
  double 
  stirrer 
  is 
  made 
  of 
  ebonite, 
  which 
  is 
  affected 
  neither 
  

   by 
  acids 
  nor 
  by 
  alkalis. 
  The 
  two 
  stirrers 
  are 
  connected 
  with 
  

   ebonite 
  rods 
  forming 
  a 
  cage 
  for 
  the 
  block 
  of 
  substance 
  to 
  be 
  

   investigated. 
  The 
  last 
  is 
  covered 
  with 
  paraffin 
  of 
  a 
  high 
  

   melting-point 
  at 
  all 
  surfaces 
  except 
  the 
  top, 
  a 
  rubber 
  ring 
  is 
  

   put 
  on 
  it 
  and 
  prevents 
  it 
  from 
  being 
  damaged 
  after 
  it 
  is 
  fixed 
  

   between 
  the 
  rods. 
  Though 
  apparently 
  little 
  work 
  had 
  to 
  be 
  

   done^ 
  I 
  found 
  that 
  to 
  get 
  constant 
  speeds 
  I 
  had 
  to 
  use 
  a 
  

   powerful 
  electromotor 
  {\ 
  H.P.) 
  to 
  prevent 
  its 
  heating 
  up, 
  and 
  

   that 
  constant 
  voltage 
  as 
  well 
  as 
  a 
  regulation 
  of 
  the 
  speed 
  had 
  to 
  

   be 
  provided 
  for. 
  Both 
  the 
  field 
  and 
  armature 
  were 
  supplied 
  

   with 
  a 
  series 
  of 
  resistances 
  and 
  with 
  continuous 
  spiral 
  resis- 
  

   tance 
  when 
  required. 
  In 
  all 
  experiments 
  I 
  usually 
  employed 
  

   200 
  volts 
  thrown 
  upon 
  the 
  common 
  terminals 
  connecting 
  the 
  

   field 
  and 
  armature. 
  For 
  the 
  variation 
  of 
  speed 
  within 
  very 
  

   great 
  limits, 
  I 
  used 
  in 
  the 
  first 
  instance 
  different 
  sets 
  of 
  

   wheels 
  of 
  different 
  diameter, 
  which 
  could 
  be 
  changed 
  as 
  

   desired, 
  and 
  the 
  wheels 
  were 
  driven 
  by 
  a 
  fiexible 
  steel 
  spiral 
  

   which 
  could 
  be 
  applied 
  to 
  all 
  of 
  them 
  by 
  means 
  of 
  the 
  

   arrangements 
  seen 
  in 
  fig. 
  2 
  (PI. 
  XYIII.) 
  . 
  To 
  get 
  the 
  varia- 
  

   tions 
  of 
  speed 
  in 
  still 
  greater 
  limits 
  the 
  volts 
  thrown 
  upon 
  the 
  

   field 
  and 
  armature 
  were 
  different, 
  use 
  being 
  made 
  of 
  accu- 
  

   mulators. 
  I 
  was 
  thus 
  able 
  to 
  change 
  the 
  speed 
  of 
  the 
  stirrer 
  

   from 
  about 
  1 
  revolution 
  per 
  minute 
  to 
  about 
  500 
  and 
  to 
  

   keep 
  the 
  speed 
  practically 
  constant. 
  The 
  best 
  results 
  were 
  

   obtained 
  for 
  speeds 
  of 
  about 
  100 
  to 
  150 
  revolutions 
  per 
  minute, 
  

   when 
  the 
  variation 
  after 
  hours 
  did 
  not 
  amount 
  to 
  1 
  revolution 
  

   per 
  minute, 
  and 
  which 
  I 
  adopted 
  for 
  my 
  investigations. 
  As 
  

   the 
  effective 
  stirring 
  depends 
  more 
  upon 
  the 
  construction 
  

   of 
  the 
  part 
  of 
  the 
  stirrer 
  in 
  the 
  liquid 
  than 
  upon 
  the 
  

   number 
  of 
  revolutions^ 
  I 
  reduced 
  the 
  last 
  by 
  improvements 
  

   in 
  the 
  first, 
  and 
  this 
  enabled 
  me 
  to 
  get 
  with 
  an 
  ordinary 
  

   one-fifth 
  second 
  stop-watch, 
  easy, 
  reliable 
  counting 
  of 
  the 
  

   number 
  of 
  revolutions 
  of 
  the 
  stirrer, 
  which 
  usually 
  were 
  kept 
  

   at 
  about 
  130 
  per 
  minute. 
  The 
  speed-indicator 
  was 
  used 
  only 
  

   for 
  speeds 
  above 
  250 
  revolutions 
  per 
  minute. 
  I 
  found 
  that 
  

   no 
  permanent 
  speed 
  could 
  be 
  got 
  for 
  longer 
  periods 
  when 
  

   ordinary 
  cords 
  are 
  used, 
  because 
  as 
  these 
  stretch 
  under 
  work 
  

   the 
  speed 
  changes 
  also. 
  A 
  thin 
  steel 
  wire 
  was 
  for 
  this 
  reason 
  

  

  