﻿542 
  Dr. 
  Meyer 
  Wilderman 
  on 
  Velocity 
  of 
  Molecular 
  

  

  this 
  way 
  in 
  getting 
  beautiful 
  uniform 
  blocks 
  free 
  from 
  air-holes 
  

   and 
  cracks 
  and 
  the 
  blocks 
  seemed 
  quite 
  excellent, 
  yet 
  when 
  

   the 
  same 
  were 
  brought 
  into 
  contact 
  with 
  H2O 
  they 
  imme- 
  

   diately 
  fell 
  to 
  pieces. 
  The 
  solids 
  on 
  coming 
  into 
  contact 
  with 
  

   H2O 
  expand 
  again 
  to 
  such 
  a 
  degree 
  that 
  they 
  fall 
  in 
  no 
  time 
  

   to 
  pieces. 
  On 
  the 
  contrary, 
  MgCOs 
  shows 
  no 
  such 
  property, 
  

   but 
  gives 
  excellent 
  blocks 
  which 
  stand 
  water 
  very 
  well. 
  

   Photo 
  7 
  gives 
  a 
  block 
  of 
  MgOOs 
  compressed 
  under 
  2500 
  

   atmospheres, 
  in 
  which 
  the 
  impression 
  of 
  the 
  piston 
  in 
  the 
  

   centre 
  is 
  still 
  to 
  be 
  seen, 
  and 
  then 
  allowed 
  to 
  remain 
  under 
  

   water. 
  Photo 
  8 
  shows 
  a 
  block 
  of 
  MgCOs, 
  which 
  was 
  com- 
  

   pressed 
  in 
  an 
  ebonite 
  lid 
  in 
  a 
  special 
  arrangement 
  by 
  means 
  

   of 
  a 
  screw, 
  after 
  it 
  was 
  first 
  mixed 
  with 
  water 
  to 
  a 
  paste, 
  and 
  

   then 
  allowed 
  to 
  remain 
  under 
  water. 
  Photo 
  9 
  shows 
  

   MgCOs 
  as 
  got 
  in 
  an 
  ebonite 
  lid 
  after 
  the 
  same 
  was 
  mixed 
  

   with 
  water 
  to 
  a 
  paste 
  and 
  dried, 
  and 
  then 
  the 
  lid 
  and 
  the 
  

   dry 
  disk 
  were 
  allowed 
  to 
  remain 
  for 
  a 
  long 
  time 
  under 
  a 
  dilute 
  

   HCl 
  solution 
  ; 
  for 
  they 
  show 
  at 
  the 
  same 
  time 
  that 
  water 
  

   does 
  not 
  break 
  up 
  the 
  same. 
  Nernst 
  and 
  Brunner 
  give 
  us, 
  

   on 
  p. 
  79 
  of 
  their 
  paper, 
  a 
  series 
  of 
  apparent 
  reasons 
  why 
  

   their 
  theory 
  does 
  not 
  require 
  to 
  hold 
  good 
  in 
  case 
  of 
  Oxides, 
  

   Carbonates, 
  &c. 
  which 
  do 
  not 
  agree 
  with 
  their 
  theory, 
  and 
  

   why 
  this 
  one 
  substance, 
  Mg(0H)2, 
  is 
  to 
  be 
  of 
  all 
  substances 
  

   tlie 
  substance 
  to 
  be 
  taken 
  for 
  the 
  test 
  of 
  their 
  theory, 
  and 
  we 
  

   are 
  invited 
  to 
  accept 
  their 
  theory 
  on 
  the 
  basis 
  of 
  " 
  Mg(0H)2 
  " 
  

   alone. 
  Now 
  we 
  find 
  that 
  Nernst 
  and 
  Brunner^s 
  so-called 
  

   Mg(0H)2 
  is 
  nothing 
  but 
  a 
  mixture 
  of 
  oxide, 
  hydroxide, 
  and 
  

   carbonate 
  of 
  magnesia. 
  Not 
  contented 
  with 
  this, 
  since 
  their 
  

   " 
  magnesium 
  hydroxide^' 
  blocks 
  do 
  not 
  hold 
  sufficiently 
  well, 
  

   they 
  mix 
  it 
  with 
  gum 
  arabicum, 
  which, 
  as 
  known, 
  is 
  the 
  

   potassium 
  and 
  calcium 
  salt 
  of 
  " 
  Arabinsaure" 
  or 
  " 
  Gumisaure,'* 
  

   and 
  so 
  their 
  mixture 
  contains 
  besides 
  also 
  the 
  Magnesium 
  

   salt 
  of 
  "Arabinsaure." 
  As 
  the 
  conditions 
  of 
  preparation 
  of 
  

   their 
  blocks 
  were 
  never 
  identical 
  in 
  respect 
  of 
  time, 
  quantity 
  

   of 
  gum 
  arabicum 
  used, 
  &c., 
  the 
  composition 
  of 
  their 
  mixture 
  

   was 
  never 
  the 
  same. 
  And 
  with 
  such 
  mixtures 
  Nernst 
  and 
  

   Brunner 
  give 
  us 
  their 
  quantitative 
  experiments 
  upon 
  speed 
  

   of 
  reaction, 
  their 
  comparative 
  experiments, 
  their 
  principal 
  

   experimental 
  proofs 
  of 
  the 
  diftiision 
  theory 
  I 
  

  

  The 
  method 
  I 
  use 
  for 
  getting 
  from 
  a 
  substance 
  chemically 
  

   pure 
  and 
  suitable 
  for 
  the 
  research, 
  blocks 
  of 
  any 
  desired 
  

   thickness, 
  of 
  the 
  same 
  uniformity 
  through 
  the 
  whole 
  of 
  its 
  

   mass, 
  free 
  from 
  air 
  and 
  cracks, 
  and 
  enabling 
  us 
  to 
  use 
  the 
  

   same 
  blocks 
  for 
  a 
  series 
  of 
  experiments 
  for 
  comparative 
  

   experiments 
  and 
  to 
  reproduce 
  the 
  same, 
  consists 
  in 
  their 
  

   artificial 
  preparation 
  under 
  the 
  very 
  high 
  j^^ressure 
  of 
  several 
  

  

  