﻿Phenomena 
  of 
  Chlorate 
  of 
  Potash 
  Crystals, 
  537 
  

  

  This 
  particular 
  crystal 
  plate 
  was 
  selected 
  from 
  a 
  very 
  large 
  

   number. 
  I 
  have 
  given 
  directions 
  for 
  preparing 
  the 
  plate 
  in 
  

   a 
  former 
  paper 
  *. 
  Possibly 
  by 
  taking 
  a 
  number 
  of 
  selected 
  

   plates 
  and 
  immersing 
  them 
  in 
  a 
  solution 
  which 
  is 
  cooling 
  off 
  

   and 
  throwing 
  down 
  crystals, 
  we 
  may 
  be 
  able 
  to 
  build 
  up 
  

   plates 
  with 
  eyen 
  larger 
  numbers 
  of 
  twin 
  planes. 
  I 
  haye 
  not 
  

   yet 
  tried 
  this 
  method. 
  If 
  somewhat 
  larger 
  plates 
  could 
  be 
  

   made 
  they 
  would 
  prove 
  superior 
  to 
  the 
  spectroscope 
  for 
  the 
  

   isolation 
  of 
  spectral 
  lines 
  for 
  monochromatic 
  illumination, 
  

   for 
  a 
  much 
  wider 
  source 
  of 
  light 
  could 
  be 
  used. 
  

  

  It 
  is 
  interesting 
  to 
  compare 
  the 
  crystal 
  described 
  in 
  this 
  

   note 
  with 
  the 
  best 
  Lippmann 
  photographs, 
  which 
  show 
  colour 
  

   resulting 
  from 
  the 
  same 
  type 
  of 
  interference. 
  

  

  Mr. 
  H. 
  E. 
  Ives 
  has 
  made 
  the 
  best 
  Lippmann 
  photographs 
  

   with 
  monochromatic 
  light 
  that 
  I 
  know 
  of. 
  The 
  spectrum 
  of 
  

   the 
  band 
  reflected 
  from 
  his 
  best 
  plate 
  is 
  shown 
  in 
  PI. 
  XY. 
  

   fig. 
  4, 
  "a/"' 
  on 
  the 
  same 
  scale 
  of 
  wave-lengths, 
  i. 
  e. 
  taken 
  with 
  

   the 
  same 
  spectroscope. 
  It 
  has 
  a 
  width 
  about 
  three 
  times 
  as 
  

   great 
  as 
  the 
  band 
  reflected 
  from 
  the 
  crystal. 
  If 
  I 
  remember 
  

   rightly, 
  Mr. 
  Ives 
  sectioned 
  a 
  similar 
  film 
  and 
  counted 
  about 
  

   250 
  silver 
  laminse, 
  built 
  up 
  by 
  the 
  stationary 
  waves. 
  This 
  is 
  

   in 
  good 
  agreement 
  with 
  our 
  estimate 
  of 
  the 
  number 
  in 
  the 
  

   chlorate 
  crystal. 
  

  

  It 
  is 
  most 
  remarkable 
  that 
  the 
  laminse 
  are 
  of 
  such 
  constant 
  

   thickness 
  in 
  a 
  given 
  plate 
  and 
  yet 
  vary 
  over 
  such 
  a 
  wide 
  

   range 
  when 
  we 
  consider 
  different 
  ; 
  a 
  plate 
  which 
  starts 
  

   with 
  twin 
  planes 
  '0002 
  mm. 
  apart 
  apparently 
  builds 
  up 
  

   700 
  laminse 
  of 
  the 
  same 
  thickness, 
  while 
  another 
  plate 
  

   starting 
  with 
  a 
  different 
  "grating 
  constant" 
  sticks 
  to 
  it 
  to 
  

   the 
  end. 
  

  

  The 
  process 
  of 
  formation 
  of 
  these 
  crystals 
  is 
  w^ell 
  worth 
  a 
  

   further 
  study. 
  It 
  would 
  be 
  very 
  interesting 
  to 
  see 
  whether 
  

   a 
  crystal 
  once 
  started 
  could 
  be 
  induced 
  to 
  change 
  its 
  mind 
  

   about 
  its 
  '• 
  constant 
  " 
  by 
  varpng 
  the 
  concentration 
  or 
  tem- 
  

   perature 
  of 
  the 
  mother 
  liquor 
  in 
  which 
  it 
  was 
  forming. 
  

  

  East 
  Hampton, 
  Long 
  Island. 
  

   July 
  1909. 
  

  

  * 
  '^ 
  Interference-colours 
  of 
  Chlorate 
  of 
  Potash 
  Crystals," 
  Phil. 
  Mag. 
  [6] 
  

   xii. 
  p. 
  67. 
  

  

  Phil 
  Mag. 
  S. 
  6. 
  Vol. 
  18. 
  Xo. 
  106. 
  Oct. 
  1909. 
  2 
  

  

  