﻿540 
  Dr. 
  Meyer 
  Wilderman 
  on 
  Velocity 
  of 
  Molecular 
  

  

  §2. 
  On 
  the 
  Method 
  of 
  Iriv 
  estimation. 
  

  

  (a) 
  On 
  the 
  artificial 
  production 
  of 
  solid 
  blocks 
  suitable 
  for 
  

   investigation 
  in 
  this 
  region. 
  Also 
  on 
  the 
  solids 
  used 
  by 
  

   Nernst 
  and 
  E. 
  Brunner 
  and 
  others 
  to 
  prove 
  the 
  Diffusion 
  

   Theory. 
  

  

  The 
  speed 
  o£ 
  reaction 
  is 
  directly 
  proportional 
  to 
  the 
  

   surface 
  of 
  the 
  solid, 
  and 
  it 
  is 
  quite 
  evident 
  that 
  no 
  reliable 
  

   research 
  at 
  a 
  constant 
  surface 
  is 
  possible, 
  and 
  still 
  less 
  are 
  

   comparative 
  quantitative 
  experiments 
  possible, 
  so 
  long 
  as 
  we 
  

   cannot 
  procure 
  a 
  solid, 
  with 
  a 
  sufficiently 
  large 
  surface, 
  which 
  

   is 
  quite 
  uniform 
  throughout 
  its 
  whole 
  thickness, 
  which 
  can 
  

   be 
  reproduced 
  every 
  time 
  we 
  want 
  it, 
  which 
  is 
  chemically 
  

   pure, 
  which 
  is 
  suitable 
  for 
  quick 
  and 
  reliable 
  measurements 
  

   of 
  concentration, 
  and 
  which 
  represents 
  a 
  reaction 
  free 
  from 
  

   subsidiary 
  reactions 
  and 
  from 
  other 
  complications. 
  To 
  get 
  

   all 
  these 
  requirements 
  realized 
  at 
  once 
  is 
  by 
  no 
  means 
  easy. 
  

   Metals 
  seem 
  to 
  answer 
  the 
  requirements 
  of 
  surface, 
  but, 
  

   except 
  Pt, 
  Ag, 
  and 
  the 
  liquid 
  mercury, 
  they 
  all 
  cannot 
  be 
  

   got 
  chemically 
  pure, 
  and 
  insurmountable 
  difficulties 
  are 
  

   created 
  for 
  correct 
  measurements 
  of 
  the 
  speed 
  of 
  reaction 
  by 
  

   the 
  interference 
  of 
  local 
  action 
  due 
  to 
  small 
  variations 
  in 
  the 
  

   impurities. 
  Again, 
  some 
  of 
  the 
  minerals, 
  such 
  as 
  marbles, 
  

   gypsums, 
  and 
  some 
  other 
  few 
  substances, 
  present 
  the 
  best 
  

   material 
  for 
  getting 
  suitable 
  blocks 
  for 
  an 
  investigation, 
  but 
  

   these 
  minerals 
  are 
  seldom 
  chemically 
  pure, 
  few 
  of 
  them 
  are 
  

   uniformly 
  the 
  same 
  everywhere, 
  and 
  still 
  fewer 
  of 
  them 
  are 
  

   substances 
  which 
  are 
  suitable 
  for 
  a 
  rapid 
  and 
  reliable 
  titration. 
  

   The 
  solid 
  substances, 
  which 
  are 
  most 
  suitable 
  and 
  desirable 
  

   for 
  research, 
  are 
  for 
  this 
  reason 
  those 
  which 
  are 
  artificially 
  

   prepared 
  in 
  the 
  laboratory, 
  but 
  the 
  difficulty 
  is 
  that 
  these 
  

   substances 
  are 
  almost 
  without 
  exception 
  obtainable 
  either 
  in 
  

   small 
  crystals 
  or 
  powders, 
  &c., 
  while 
  we 
  require 
  for 
  the 
  inve.'^ti- 
  

   gation 
  blocks 
  with 
  large 
  surfaces. 
  How 
  Nernst 
  and 
  Brunner 
  

   try 
  to 
  overcome 
  the 
  difficulties 
  here 
  is 
  best 
  to 
  be 
  seen 
  from 
  

   the 
  two 
  princvpcd 
  substances 
  of 
  their 
  investigation, 
  upon 
  which 
  

   they 
  tried 
  to 
  build 
  up 
  experimentally 
  their 
  diffusion 
  theory, 
  

   namely, 
  benzoic 
  acid 
  and 
  " 
  magnesium 
  hydroxide.^'' 
  

  

  About 
  the 
  first 
  we 
  read 
  that, 
  to 
  create 
  a 
  block, 
  they 
  

   " 
  melted 
  the 
  benzoic 
  acid 
  in 
  a 
  test-tube, 
  poured 
  it 
  into 
  a 
  

   porcelain 
  cover 
  of 
  a 
  crucible, 
  5 
  cm. 
  diameter. 
  On 
  cooling 
  

   the 
  same 
  separated 
  from 
  the 
  cover, 
  and 
  they 
  fixed 
  it 
  in 
  again 
  

   with 
  shellac 
  ; 
  the 
  surface 
  was 
  then 
  rubbed 
  down 
  with 
  a 
  

   knife 
  and 
  sandpaper. 
  The 
  surface 
  still 
  clearly 
  retained 
  its 
  

   crystalline 
  structure. 
  This 
  cake 
  still 
  contained 
  scratches 
  at 
  

   the 
  rim, 
  and 
  they 
  filled 
  these 
  now 
  up 
  with 
  paraffin.''' 
  With 
  

  

  