﻿544 
  Dr. 
  Meyer 
  Wilderman 
  on 
  Velocity 
  of 
  Molecular 
  

  

  during 
  two 
  hours. 
  The 
  surface 
  is 
  still 
  excellent. 
  I 
  find, 
  

   however, 
  that 
  while 
  some 
  o£ 
  them 
  (such 
  as 
  benzoic 
  acid, 
  

   most 
  organic 
  substances, 
  MgCOs, 
  &c.) 
  remain 
  on 
  placing 
  

   the 
  disk 
  into 
  water 
  (under 
  stirring) 
  in 
  perfect 
  condition; 
  

   others, 
  such 
  as 
  Mg(0H)2, 
  Fe2(OH)6, 
  & 
  ,, 
  break 
  up 
  mecha- 
  

   nically 
  at 
  once, 
  since 
  when 
  the 
  disks 
  are 
  brought 
  into 
  

   contact 
  with 
  water 
  they 
  suffer 
  too 
  great 
  an 
  expansion. 
  

   All 
  the 
  same, 
  the 
  above 
  method 
  now 
  opens 
  the 
  way 
  for 
  a 
  

   true 
  and 
  reliable 
  investigation 
  in 
  this 
  region, 
  putting 
  at 
  our 
  

   disposal 
  an 
  exceedingly 
  great 
  number 
  of 
  chemically 
  pure 
  

   substances, 
  suitable 
  and 
  desirable 
  for 
  this 
  research, 
  while 
  

   before 
  we 
  practically 
  had 
  none, 
  and 
  we 
  were 
  dependent 
  upon 
  

   minerals, 
  which 
  are 
  seldom 
  perfectly 
  pure. 
  Care 
  was 
  taken 
  

   to 
  use 
  only 
  the 
  purest 
  chemicals 
  for 
  this 
  research, 
  and 
  the 
  

   firm 
  of 
  Merck 
  prepared 
  the 
  same 
  for 
  me 
  with 
  special 
  care 
  

   and 
  under 
  special 
  instructions 
  ; 
  and 
  where 
  minerals 
  had 
  for 
  

   special 
  reasons 
  to 
  be 
  used, 
  only 
  the 
  best 
  and 
  purest 
  specimens 
  

   procurable 
  were 
  employed. 
  

  

  (b) 
  On 
  the 
  Arrangement 
  of 
  Constant 
  Speeds 
  of 
  Stirrer, 
  

  

  If 
  we 
  have 
  a 
  super-cooled 
  or 
  a 
  super-saturated 
  solution, 
  so 
  

   that 
  very 
  fine 
  particles 
  of 
  ice 
  or 
  salt 
  separate 
  from 
  the 
  

   whole 
  of 
  the 
  liquid, 
  and 
  through 
  the 
  whole 
  of 
  the 
  liquid, 
  

   then, 
  by 
  the 
  use 
  of 
  an 
  effective 
  stirrer 
  creating 
  currents 
  in 
  

   all 
  directions, 
  a 
  Qniform 
  state 
  of 
  the 
  whole 
  system 
  during 
  

   the 
  reaction 
  can 
  be 
  obtained, 
  as 
  can 
  be 
  seen 
  from 
  the 
  photo- 
  

   graphic 
  curves 
  in 
  my 
  paper 
  (Zeitsclir. 
  fiir 
  pJii/s. 
  CJiemie, 
  1899) 
  

   giving 
  the 
  speed 
  of 
  these 
  reactions. 
  When, 
  however, 
  we 
  

   have 
  a 
  solid 
  piece, 
  salt 
  or 
  ice 
  in 
  a 
  liquid 
  mass, 
  so 
  that 
  the 
  

   contact 
  between 
  the 
  solid 
  and 
  the 
  liquid 
  is 
  only 
  local, 
  and 
  

   reduced 
  to 
  a 
  comparatively 
  very 
  small 
  surface 
  of 
  contact, 
  it 
  

   is 
  extremely 
  difficult 
  to 
  get 
  the 
  liquid 
  uniform 
  through 
  the 
  

   whole 
  mass, 
  as 
  already 
  mentioned 
  in 
  the 
  above 
  paper. 
  Nernst 
  

   and 
  Brunner 
  use 
  an 
  air-motor, 
  which 
  is 
  known 
  to 
  be 
  inconstant, 
  

   and 
  the 
  variations 
  of 
  its 
  speed 
  were, 
  according 
  to 
  Nernst 
  

   and 
  Brunner, 
  as 
  much 
  as 
  10, 
  15, 
  sometimes 
  even 
  30 
  percent. 
  

   The 
  direct 
  experiments 
  with 
  pieces 
  of 
  rubber, 
  of 
  the 
  same 
  

   specific 
  gravity 
  as 
  water, 
  showed 
  me, 
  that 
  if 
  we 
  keep 
  the 
  

   solid 
  fixed 
  at 
  the 
  bottom 
  and 
  move 
  the 
  liquid 
  by 
  the 
  stirrer, 
  

   the 
  number 
  of 
  revolutions 
  which 
  the 
  liquid 
  makes 
  past 
  

   the 
  solid 
  is 
  not 
  directly 
  proportional 
  to 
  the 
  number 
  of 
  revolu- 
  

   tions 
  of 
  the 
  stirrer, 
  but 
  is 
  considerably 
  smaller. 
  The 
  liquid 
  

   is 
  also 
  never 
  equally 
  moved 
  in 
  all 
  its 
  layers, 
  as 
  is 
  to 
  be 
  seen 
  

   from 
  the 
  fact, 
  that 
  a 
  cone 
  is 
  formed 
  in 
  it 
  with 
  the 
  apex 
  

   (smallest 
  speed) 
  on 
  the 
  stem 
  of 
  the 
  stirrer, 
  and 
  the 
  base 
  

   (biggest 
  speed) 
  above 
  it, 
  which 
  is 
  the 
  higher 
  the 
  quicker 
  the 
  

  

  