﻿Chemistry 
  and 
  Physics. 
  375 
  

  

  SCIENTIFIC 
  INTELLIGENCE. 
  

  

  I. 
  Chemistry 
  and 
  Physics. 
  

  

  1. 
  Analytical 
  Weighing. 
  — 
  Since 
  it 
  appears 
  that 
  many 
  chem- 
  

   ists 
  at 
  the 
  present 
  time 
  regard 
  the 
  nse 
  of 
  long 
  swings 
  of 
  the 
  

   analytical 
  balance 
  as 
  the 
  best 
  and 
  most 
  accurate 
  method 
  of 
  

   weighing, 
  since 
  many 
  recent 
  text-books 
  on 
  quantitative 
  analysis 
  

   advocate 
  this 
  process, 
  sometimes 
  without 
  even 
  mentioning 
  a 
  

   simpler 
  method, 
  and 
  since 
  the 
  teaching 
  of 
  long 
  swing 
  weighing 
  

   has 
  evidently 
  grown 
  in 
  favor 
  in 
  recent 
  times, 
  Horace 
  L. 
  Wells, 
  

   of 
  the 
  Sheffield 
  Scientific 
  School, 
  has 
  discussed 
  methods 
  of 
  weigh- 
  

   ing 
  and 
  has 
  presented 
  a 
  plea 
  for 
  the 
  general 
  use 
  of 
  short 
  swings 
  

   of 
  the 
  balance 
  in 
  weighing. 
  

  

  He 
  argues 
  that 
  the 
  long 
  swing 
  presents 
  no 
  greater 
  absolute 
  

   variation 
  than 
  a 
  short 
  one 
  for 
  the 
  same 
  difference 
  in 
  weight, 
  

   because 
  the 
  balance 
  acts 
  as 
  a 
  pendulum 
  and 
  hence 
  tends 
  to 
  swing 
  

   equal 
  distances 
  on 
  each 
  side 
  of 
  the 
  point 
  of 
  rest, 
  whether 
  the 
  

   swings 
  are 
  long 
  or 
  short. 
  With 
  short 
  swings 
  the 
  point 
  of 
  equi- 
  

   librium 
  may 
  be 
  readily 
  observed 
  as 
  the 
  middle 
  point 
  of 
  the 
  

   swing, 
  but 
  with 
  very 
  long 
  swings 
  there 
  is 
  a 
  large 
  retardation 
  in 
  

   each 
  movement 
  and 
  a 
  series 
  of 
  observations, 
  with 
  a 
  complicated 
  

   calculation, 
  is 
  required 
  to 
  find 
  the 
  point 
  of 
  equilibrium. 
  The 
  

   long 
  swings 
  cannot 
  be 
  read 
  as 
  easily 
  and 
  accurately 
  as 
  short 
  ones 
  

   on 
  account 
  of 
  the 
  more 
  rapid 
  movement 
  of 
  the 
  former. 
  The 
  

   calculation 
  of 
  the 
  point 
  of 
  equilibrium 
  from 
  long-swing 
  readings 
  

   is 
  mathematically 
  inexact, 
  because 
  the 
  retardation 
  diminishes 
  

   with 
  the 
  length 
  of 
  the 
  swing 
  while 
  the 
  means 
  of 
  the 
  values 
  on 
  

   each 
  side 
  are 
  used 
  in 
  the 
  calculation. 
  For 
  instance, 
  with 
  a 
  re- 
  

   tardation 
  of 
  14 
  of 
  the 
  distance 
  from 
  the 
  starting 
  point 
  to 
  the 
  

   center, 
  the 
  latter 
  being 
  the 
  point 
  of 
  rest, 
  the 
  swings 
  + 
  10" 
  0, 
  

   — 
  7-5, 
  -f- 
  5-6, 
  — 
  4-2, 
  + 
  3-2 
  are 
  calculated, 
  which 
  give 
  the 
  point 
  of 
  

   equilibrium 
  as 
  + 
  0-4 
  instead 
  of 
  the 
  correct 
  point, 
  0; 
  whereas 
  

   swings 
  -gV 
  the 
  length 
  of 
  the 
  others 
  would 
  give 
  the 
  readings 
  + 
  0-5, 
  

   — 
  0-4, 
  + 
  0-3, 
  — 
  0-2, 
  -f- 
  0-2 
  from 
  which 
  the 
  true 
  center 
  would 
  

   be 
  . 
  readily 
  indicated 
  by 
  observation. 
  The 
  article 
  presents 
  sev- 
  

   eral 
  other 
  arguments 
  against 
  the 
  use 
  of 
  long 
  swings, 
  but 
  these 
  

   need 
  not 
  be 
  mentioned 
  here. 
  

  

  The 
  conclusion 
  of 
  the 
  article 
  is 
  as 
  follows 
  : 
  

  

  ' 
  ' 
  If 
  the 
  arguments 
  presented 
  here 
  are 
  sound, 
  as 
  they 
  appear 
  to 
  

   be, 
  it 
  is 
  certainly 
  very 
  remarkable 
  that 
  many 
  chemists 
  have 
  con- 
  

   sidered 
  it 
  desirable 
  to 
  force 
  the 
  reluctant 
  analytical 
  balance, 
  

   when 
  close 
  to 
  equilibrium, 
  to 
  give 
  long 
  swings, 
  in 
  place 
  of 
  its 
  

   natural 
  short 
  ones, 
  in 
  order 
  to 
  do 
  a 
  vast 
  amount 
  of 
  useless 
  work. 
  

   The 
  suspicion 
  is 
  unavoidable 
  that 
  the 
  simple 
  pendulum 
  principle 
  

   of 
  the 
  balance 
  has 
  been 
  lost 
  sight 
  of 
  in 
  the 
  entirely 
  false 
  expecta- 
  

   tion 
  that 
  the 
  absolute 
  variation 
  of 
  a 
  swing 
  would 
  be 
  increased 
  by 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XLIX, 
  No. 
  293.— 
  May, 
  1920. 
  

  

  27 
  

  

  