﻿Determination 
  of 
  Potassium 
  Sjiectroscopically. 
  453 
  

  

  merits 
  looking 
  in 
  this 
  direction 
  we 
  found 
  it 
  best, 
  for 
  our 
  pur- 
  

   pose 
  at 
  least, 
  to 
  fall 
  back 
  upon 
  Truchot's 
  method 
  of 
  comparing 
  

   visible 
  lines, 
  rather 
  than 
  to 
  try 
  to 
  fix 
  the 
  vanishing 
  point 
  or 
  

   the 
  point 
  of 
  extinction 
  of 
  the 
  spectral 
  line. 
  We 
  chose 
  a 
  dilu- 
  

   tion 
  of 
  the 
  standard 
  solution 
  which 
  corresponds 
  to 
  the 
  presence 
  

   of 
  -g-i-p- 
  mg. 
  of 
  potassium 
  to 
  the 
  coil-full, 
  and 
  set 
  the 
  slit 
  at 
  a 
  width 
  

   of 
  0-23 
  mm 
  , 
  having 
  found 
  it 
  most 
  advantageous 
  to 
  work 
  with 
  

   lines 
  for 
  comparison 
  bright 
  enough 
  to 
  be 
  visible 
  without 
  much 
  

   effort 
  Our 
  mode 
  of 
  proceeding 
  is 
  to 
  dilute 
  the 
  test-solution 
  

   until 
  the 
  line 
  given 
  by 
  the 
  potassium 
  contained 
  in 
  a 
  coil-full 
  is 
  

   of 
  the 
  same 
  brightness 
  as 
  that 
  given 
  by 
  the 
  same 
  quantity 
  of 
  

   the 
  standard 
  solution. 
  From 
  the 
  final 
  volume 
  of 
  the 
  test- 
  

   solution 
  the 
  quantity 
  of 
  potassium 
  present 
  in 
  it 
  is 
  directly 
  cal- 
  

   culable 
  ; 
  for, 
  since 
  any 
  given 
  volume 
  of 
  the 
  test-solution 
  at 
  its 
  

   final 
  dilution 
  contains 
  exactly 
  the 
  same 
  amount 
  of 
  potassium 
  as 
  

   the 
  same 
  volume 
  of 
  the 
  standard 
  solution, 
  we 
  have 
  only 
  to 
  

   multiply 
  the 
  number 
  expressing 
  the 
  volume 
  in 
  cubic 
  centime- 
  

   ters 
  of 
  the' 
  test-solution 
  by 
  the 
  weight 
  in 
  grams 
  of 
  the 
  potas- 
  

   sium 
  contained 
  in 
  one 
  cubic 
  centimeter 
  of 
  the 
  standard 
  in 
  

   order 
  to 
  obtain 
  the 
  weight 
  in 
  grams 
  of 
  potassium 
  in 
  the 
  whole 
  

   test-solution. 
  We 
  found 
  it 
  convenient 
  to 
  use 
  several 
  coils 
  

   adjusted 
  to 
  the 
  same 
  capacity, 
  and 
  to 
  clean, 
  fill, 
  dry 
  and' 
  ignite 
  

   them 
  before 
  the 
  spectroscope 
  in 
  the 
  manner 
  previously 
  de- 
  

   scribed. 
  From 
  time 
  to 
  time 
  the 
  capacity 
  of 
  the 
  coils 
  should 
  

   be 
  readjusted, 
  or 
  else 
  the 
  final 
  comparison 
  tests 
  should 
  be 
  made 
  

   with 
  a 
  single 
  coil. 
  It 
  is 
  essential 
  that 
  the 
  eye 
  of 
  the 
  observer 
  

   should 
  be 
  kept 
  as 
  nearly 
  as 
  possible 
  in 
  the 
  same 
  condition 
  of 
  

   sensitiveness 
  and 
  in 
  the 
  same 
  position 
  in 
  making 
  the 
  compari- 
  

   sons, 
  and 
  to 
  accomplish 
  this 
  end 
  we 
  found 
  it 
  best 
  to 
  hold 
  the 
  

   eye 
  at 
  the 
  observing 
  telescope 
  during 
  the 
  entire 
  interval 
  be- 
  

   tween 
  the 
  exposures, 
  to 
  shade 
  it 
  carefully 
  by 
  the 
  hand, 
  or 
  

   otherwise, 
  to 
  cover 
  the 
  eye 
  not 
  in 
  use, 
  to 
  cut 
  off 
  all 
  direct 
  sun- 
  

   light 
  from 
  the 
  work-table 
  (though 
  the 
  diffused 
  light 
  of 
  the 
  

   room 
  is 
  not 
  objectionable), 
  and 
  to 
  light 
  the 
  comparison 
  scale 
  of 
  

   the 
  spectroscope 
  to 
  the 
  faintest 
  possible 
  visibility 
  in 
  order 
  to 
  

   fix 
  exactly 
  the 
  position 
  in 
  which 
  the 
  line 
  is 
  to 
  be 
  sought. 
  It 
  

   is 
  important, 
  too, 
  that 
  the 
  trials 
  of 
  the 
  test 
  and 
  standard 
  

   should 
  come 
  as 
  closely 
  together 
  as 
  possible 
  in 
  point 
  of 
  time. 
  

   The 
  observations 
  of 
  a 
  series 
  should 
  be 
  made 
  by 
  the 
  same 
  indi- 
  

   vidual, 
  the 
  preparation 
  and 
  exposure 
  of 
  the 
  wires 
  being 
  made 
  

   by 
  another. 
  It 
  is 
  not 
  possible 
  to 
  attain 
  the 
  best 
  results 
  in 
  such 
  

   work 
  single 
  handed. 
  The 
  dilution 
  of 
  the 
  test-solution 
  is 
  made 
  

   conveniently, 
  and 
  with 
  sufficient 
  accuracy, 
  in 
  100cm. 
  3 
  cylinders 
  

   graduated 
  to 
  half 
  cubic 
  centimeters, 
  the 
  mixture 
  being 
  made 
  

   thorough 
  by 
  passing 
  the 
  solution 
  from 
  vessel 
  to 
  vessel. 
  It 
  is 
  

   often 
  advantageous 
  to 
  divide 
  a 
  liquid 
  which 
  is 
  to 
  be 
  diluted 
  

   and 
  to 
  work 
  with 
  aliquot 
  portions, 
  so 
  that 
  it 
  may 
  be 
  possible 
  to 
  

  

  