﻿Determination 
  of 
  Potassium 
  Speetroscopically. 
  451 
  

  

  It 
  is 
  obvious 
  from 
  these 
  results 
  that 
  a 
  considerable 
  amount 
  

   of 
  sodium 
  may 
  be 
  present 
  in 
  the 
  flame, 
  when 
  the 
  sodium 
  line 
  

   is 
  in 
  full 
  view 
  in 
  the 
  spectrum, 
  and 
  the 
  slit 
  adjusted 
  to 
  nearly 
  

   the 
  lowest 
  limit 
  of 
  visibility 
  of 
  pure 
  potassium, 
  without 
  inter- 
  

   fering 
  with 
  the 
  appearance 
  of 
  the 
  potassium 
  line, 
  but 
  that 
  a 
  

   quantity 
  of 
  sodium 
  amounting 
  to 
  a 
  hundred 
  times 
  that 
  of 
  the 
  

   potassium 
  is 
  sufficient 
  to 
  entirely 
  overpower 
  the 
  spectrum 
  of 
  

   the 
  potassium. 
  The 
  inference 
  is 
  plain 
  that 
  the 
  proportion 
  of 
  

   sodium 
  to 
  potassium 
  should 
  not 
  be 
  permitted 
  to 
  reach 
  100 
  : 
  I 
  

   when 
  it 
  is 
  desirable 
  to 
  bring 
  out 
  the 
  full 
  delicacy 
  of 
  the 
  spec- 
  

   troscopic 
  test 
  with 
  the 
  sodium 
  line 
  in 
  the 
  held 
  of 
  view. 
  

   When 
  too 
  great 
  a 
  proportion 
  of 
  sodium 
  is 
  present, 
  its 
  influ- 
  

   ence 
  may 
  be 
  moderated 
  by 
  throwing 
  the 
  sodium 
  line 
  out 
  of 
  

   view, 
  if 
  the 
  instrument 
  in 
  use 
  possesses 
  the 
  necessary 
  adjust- 
  

   ment 
  ; 
  otherwise, 
  it 
  is 
  easy 
  to 
  effect 
  a 
  partial 
  separation 
  of 
  the 
  

   sodium 
  chloride 
  from 
  the 
  potassium 
  chloride, 
  before 
  bringing 
  

   the 
  solution 
  to 
  the 
  test, 
  by 
  precipitating 
  with 
  alcohol. 
  Our 
  

   experience 
  shows 
  that 
  the 
  delicacy 
  of 
  the 
  test 
  for 
  potassium 
  

   is 
  not 
  impaired 
  materially 
  by 
  such 
  treatment 
  of 
  the 
  mixed 
  

   chlorides. 
  We 
  found, 
  for 
  example, 
  that 
  O'OOTO 
  grm. 
  of 
  potas- 
  

   sium 
  chloride 
  mixed 
  with 
  5 
  grm. 
  of 
  pure 
  sodium 
  chloride, 
  

   dissolved 
  in 
  the 
  least 
  amount 
  of 
  water, 
  and 
  extracted 
  carefully 
  

   by 
  about 
  7 
  cm. 
  3 
  of 
  absolute 
  alcohol 
  applied 
  in 
  successive 
  por- 
  

   tions, 
  was 
  so 
  completely 
  retained 
  in 
  solution 
  and 
  separated 
  

   from 
  sodium, 
  that 
  a 
  coil- 
  full 
  taken 
  from 
  the 
  solution 
  diluted 
  

   to 
  140 
  cm. 
  3 
  gave 
  the 
  spectroscopic 
  test 
  for 
  potassium 
  distinctly 
  

   with 
  the 
  slit 
  at 
  0*23 
  mm. 
  In 
  this 
  case, 
  at 
  least, 
  the 
  treatment 
  

   did 
  not 
  diminish 
  the 
  delicacy 
  of 
  the 
  test 
  ; 
  for, 
  a 
  coil-full 
  of 
  

   the 
  diluted 
  solution 
  could 
  not 
  have 
  contained 
  more 
  than 
  y-oVo 
  

   mg. 
  of 
  potassium, 
  if 
  nothing 
  had 
  been 
  lost. 
  It 
  was 
  found, 
  in 
  

   like 
  manner, 
  that, 
  by 
  taking 
  pains 
  to 
  evaporate 
  the 
  alcoholic 
  

   extract, 
  and 
  to 
  dissolve 
  the 
  residue 
  in 
  a 
  drop 
  of 
  water, 
  0001 
  

   grm. 
  of 
  potassium 
  originally 
  present 
  as 
  the 
  chloride 
  with 
  0*5 
  

   grm. 
  of 
  sodium 
  chloride, 
  was 
  easily 
  found. 
  By 
  turning 
  the 
  

   observing 
  telescope 
  so 
  as 
  to 
  cut 
  off 
  as 
  completely 
  as 
  possible 
  

   the 
  sodium 
  light 
  we 
  were 
  able 
  to 
  detect 
  potassium 
  in 
  four 
  suc- 
  

   cessive 
  tests 
  of 
  a 
  drop 
  of 
  the 
  final 
  solution 
  which 
  was 
  just 
  

   large 
  enough 
  to 
  fill 
  the 
  coil 
  four 
  times, 
  when 
  the 
  original 
  

   amount 
  of 
  potassium 
  present 
  with 
  0*5 
  grm. 
  of 
  sodium 
  chloride 
  

   was 
  0*00001 
  grm. 
  This 
  is 
  equivalent 
  to 
  detecting 
  -^-§ 
  mg. 
  of 
  

   potassium 
  in 
  a 
  drop 
  large 
  enough 
  to 
  fill 
  the 
  coil 
  once. 
  We 
  

   were 
  assured 
  of 
  the 
  entire 
  absence 
  of 
  potassium 
  from 
  the 
  

   sodium 
  chloride 
  which 
  we 
  used 
  by 
  the 
  fact 
  that 
  the 
  similar 
  

   extraction 
  of 
  1 
  grm. 
  of 
  the 
  salt 
  by 
  alcohol 
  left 
  a 
  residue 
  which 
  

   yielded 
  no 
  line 
  of 
  potassium 
  when 
  examined 
  spectroscopically. 
  

   It 
  is 
  perhaps 
  worth 
  noting 
  in 
  passing 
  that 
  the 
  coil 
  may 
  be 
  

  

  