﻿Chemistry 
  and 
  Physics. 
  69 
  

  

  2. 
  The 
  Atomic 
  Weight 
  of 
  Carbon. 
  — 
  An 
  elaborate 
  series 
  of 
  

   determinations 
  of 
  the 
  normal 
  density 
  of 
  ethylene 
  gas, 
  C^H^ 
  has 
  

   been 
  carried 
  out 
  by 
  T. 
  Batuecas 
  under 
  the 
  direction 
  of 
  Profes- 
  

   sor 
  Guye 
  at 
  Geneva. 
  The 
  gas 
  was 
  prepared 
  from 
  alcohol 
  by 
  

   several 
  different 
  methods 
  and 
  the 
  agreements 
  of 
  the 
  results 
  were 
  

   remarkably 
  close. 
  The 
  mean 
  of 
  21 
  measurements 
  gave 
  1-2603 
  

   ± 
  0-0001 
  g. 
  as 
  the 
  weight 
  of 
  a 
  liter 
  under 
  normal 
  conditions. 
  

   From 
  this 
  result 
  the 
  molecular 
  weight 
  of 
  the 
  gas 
  and 
  the 
  con- 
  

   sequent 
  atomic 
  weight 
  of 
  carbon 
  were 
  calculated 
  by 
  the 
  usual 
  

   physico-chemical 
  methods, 
  either 
  that 
  of 
  molecular 
  volumes 
  

   according 
  to 
  Leduc, 
  that 
  of 
  limiting 
  densities 
  according 
  to 
  Eay- 
  

   leigh 
  and 
  Berthelot, 
  or 
  that 
  of 
  Guye 
  based 
  upon 
  the 
  critical 
  

   constants. 
  The 
  results 
  thus 
  obtained 
  were 
  11-996, 
  11-999 
  and 
  

   12-005 
  for 
  the 
  atomic 
  weight 
  of 
  carbon, 
  which 
  agree 
  closely 
  with 
  

   the 
  value 
  calculated 
  by 
  Clarke 
  and 
  by 
  Guye, 
  and 
  with 
  the 
  

   value 
  12- 
  00 
  for 
  a 
  long 
  time 
  accepted 
  in 
  the 
  international 
  table. 
  

   It 
  is 
  considered 
  inopportune 
  that 
  a 
  change 
  in 
  this 
  atomic 
  weight 
  

   to 
  12- 
  005 
  was 
  made 
  by 
  the 
  international 
  committee 
  in 
  1917.— 
  

   Jour. 
  Chem.-Phys., 
  16, 
  322. 
  h. 
  l. 
  w. 
  

  

  3. 
  The 
  Acidimetry 
  of 
  Colored 
  Solutions. 
  — 
  Having 
  occasion 
  

   to 
  titrate 
  alkaloidal 
  solutions 
  containing 
  much 
  coloring 
  matter, 
  

   Alfred 
  Tingle, 
  of 
  Toronto, 
  was 
  unable 
  to 
  apply 
  the 
  method 
  pro- 
  

   posed 
  by 
  A. 
  H. 
  Allen, 
  consisting 
  in 
  dissolving 
  the 
  base 
  and 
  

   impurity 
  in 
  an 
  immiscible 
  solvent 
  and 
  then 
  adding 
  standard 
  acid 
  

   until 
  methyl 
  orange 
  in 
  the 
  aqueous 
  layer 
  showed 
  an 
  acid 
  reac- 
  

   tion, 
  since 
  the 
  coloring-matter 
  interfered 
  even 
  with 
  this 
  method, 
  

   but 
  he 
  was 
  able 
  to 
  overcome 
  the 
  difficulty 
  in 
  finding 
  the 
  neutral 
  

   point 
  by 
  titrating 
  directly 
  and 
  using 
  a 
  pocket 
  spectroscope 
  for 
  

   nnding 
  the 
  neutral 
  point. 
  A 
  direct 
  vision 
  diffraction 
  instrument 
  

   gave 
  satisfactory 
  results 
  when 
  applied 
  to 
  five 
  different 
  common 
  

   indicators. 
  Blank 
  experiments 
  are 
  necessary 
  in 
  order 
  to 
  find 
  

   the 
  end-points 
  of 
  most 
  indicators. 
  Usually 
  the 
  breadth 
  of 
  an 
  

   absorption 
  band 
  is 
  changed 
  when 
  the 
  solution 
  becomes 
  alkaline. 
  

   The 
  concentration 
  of 
  most 
  indicators 
  is 
  desirably 
  greater 
  when 
  

   used 
  with 
  the 
  spectroscope 
  than 
  when 
  used 
  ordinarily. 
  The 
  

   observations 
  may 
  be 
  made 
  through 
  a 
  conical 
  flask 
  or 
  a 
  vial 
  with 
  

   flat 
  sides, 
  but 
  the 
  layer 
  of 
  liquid 
  must 
  not 
  be 
  too 
  great 
  to 
  pre- 
  

   vent 
  the 
  admission 
  of 
  a 
  satisfactory 
  amount 
  of 
  light. 
  It 
  appears 
  

   that 
  this 
  method 
  will 
  be 
  useful 
  in 
  many 
  practical 
  cases. 
  — 
  Jour. 
  

   Amer. 
  Chem. 
  Soc., 
  40, 
  873. 
  h. 
  l. 
  w. 
  

  

  4. 
  The 
  Determination 
  of 
  Nitrites. 
  — 
  M. 
  F. 
  Dlenert 
  has 
  devised 
  

   a 
  method 
  for 
  this 
  purpose 
  for 
  use 
  in 
  cases 
  where 
  the 
  amount 
  of 
  

   nitrite 
  present 
  is 
  larger 
  than 
  convenient 
  for 
  the 
  application 
  of 
  

   the 
  usual 
  colorimetric 
  tests. 
  The 
  method 
  is 
  based 
  upon 
  the 
  

   liberation 
  of 
  iodine 
  by 
  the 
  well-known 
  reaction 
  expressed 
  by 
  the 
  

   equation 
  

  

  NaN0 
  2 
  + 
  2HI 
  = 
  Nal 
  + 
  I 
  + 
  NO 
  + 
  H 
  2 
  

   and 
  then 
  measuring 
  the 
  liberated 
  iodine 
  by 
  means 
  of 
  arsenious 
  

  

  