﻿328 
  v 
  Scientific 
  Intelligence. 
  

  

  In 
  order 
  to 
  determine 
  the 
  delicacy 
  of 
  the 
  method 
  a 
  mixture 
  

   of 
  very 
  finely 
  powdered 
  silicon 
  carbide 
  ("carborundum'") 
  and 
  

   aluminium 
  oxide, 
  prepared 
  by 
  igniting 
  the 
  hydroxide 
  in 
  oxygen, 
  

   was 
  made, 
  containing 
  9 
  990 
  g. 
  of 
  alumina 
  and 
  0*01 
  g. 
  of 
  the 
  car- 
  

   bide. 
  The 
  mixture 
  was 
  heated 
  for 
  an 
  hour 
  in 
  oxygen 
  to 
  burn 
  

   out 
  all 
  carbon 
  compounds 
  except 
  silicon 
  carbide, 
  and 
  it 
  was 
  care- 
  

   fully 
  protected 
  from 
  atmospheric 
  dust. 
  

  

  Experiments 
  were 
  then 
  made 
  by 
  fusing 
  varying 
  quantities 
  of 
  

   the 
  mixture 
  with 
  lead 
  chromate 
  in 
  sealed 
  tubes 
  containing 
  in 
  

   each 
  case 
  a 
  drop 
  of 
  saturated 
  barium 
  hydroxide 
  solution 
  in 
  a 
  

   small 
  depression 
  blown 
  near 
  the 
  open 
  end, 
  and 
  provided 
  at 
  this 
  

   end 
  with 
  an 
  attached 
  protective 
  tube 
  containing 
  solid 
  potassium 
  

   hydroxide. 
  The 
  following 
  results 
  were 
  obtained 
  with 
  different 
  

   weights 
  of 
  the 
  mixture 
  : 
  

  

  100 
  mg. 
  gave 
  an 
  abundant 
  white 
  film. 
  

   20 
  mg. 
  gave 
  a 
  distinct 
  white 
  film. 
  

   14 
  mg. 
  gave 
  a 
  slight 
  but 
  distinct 
  white 
  film. 
  

   10 
  mg. 
  gave 
  a 
  very 
  faint 
  white 
  film. 
  

   8 
  mg. 
  gave 
  a 
  doubtful 
  result. 
  

   4 
  mg. 
  gave 
  absolutely 
  no 
  result. 
  

   1*5 
  mg. 
  gave 
  absolutely 
  no 
  result. 
  

  

  Ten 
  milligrams 
  of 
  the 
  mixture 
  was 
  the 
  smallest 
  amount 
  that 
  

   gave 
  an 
  unquestionable 
  reaction. 
  This 
  corresponds 
  to 
  0*01 
  mg. 
  

   of 
  silicon 
  carbide 
  containing 
  003 
  mg. 
  of 
  carbon. 
  Undoubtedly 
  

   smaller 
  amounts 
  of 
  carbon 
  may 
  be 
  detected 
  by 
  using 
  a 
  minute 
  

   drop 
  of 
  solution 
  of 
  barium 
  hydroxide 
  and 
  observing 
  the 
  result 
  

   with 
  a 
  microscope. 
  In 
  doubtful 
  cases 
  a 
  blank 
  test 
  should 
  be 
  

   made 
  for 
  comparison. 
  — 
  Jour. 
  Amer. 
  Chem. 
  JSoc, 
  xxxix, 
  374. 
  

  

  h. 
  l. 
  w. 
  

  

  2. 
  A 
  JVetv 
  Volumetric 
  Method 
  for 
  the 
  Determination 
  of 
  

   Cobalt. 
  — 
  W. 
  D. 
  Engle 
  and 
  R. 
  G. 
  Gustavson 
  have 
  devised 
  a 
  

   method 
  for 
  the 
  determination 
  of 
  cobalt 
  when 
  nickel 
  is 
  present, 
  

   which 
  according 
  to 
  their 
  test-analyses 
  gives 
  excellent 
  results. 
  

   Metals 
  of 
  the 
  copper 
  and 
  iron 
  groups 
  as 
  well 
  as 
  manganese 
  must 
  

   be 
  first 
  removed 
  by 
  the 
  usual 
  methods, 
  and 
  while 
  zinc, 
  the 
  alkali, 
  

   and 
  the 
  alkali-earth 
  metals 
  may 
  be 
  present, 
  the 
  solution 
  must 
  

   contain 
  nothing 
  that 
  will 
  liberate 
  iodine 
  in 
  acid 
  solution. 
  

  

  To 
  about 
  100 
  cc 
  of 
  the 
  solution 
  containing 
  about 
  5 
  CC 
  of 
  dilute 
  

   sulphuric 
  acid 
  in 
  excess, 
  1 
  or 
  2 
  g. 
  of 
  solid 
  sodium 
  perborate 
  are 
  

   added, 
  and 
  after 
  this 
  has 
  dissolved 
  an 
  excess 
  of 
  sodium 
  hydroxide 
  

   is 
  added 
  and 
  the 
  liquid 
  is 
  boiled 
  for 
  10 
  minutes. 
  The 
  mixture 
  is 
  

   then 
  cooled 
  to 
  room 
  temperature, 
  and 
  after 
  1 
  g. 
  of 
  potassium 
  

   iodide 
  has 
  been 
  added 
  it 
  is 
  acidified 
  with 
  dilute 
  sulphuric 
  acid, 
  

   and 
  finalh 
  7 
  after 
  the 
  precipitate 
  has 
  dissolved 
  the 
  free 
  iodine 
  is 
  

   titrated 
  with 
  sodium 
  thiosulphate 
  solution 
  with 
  starch 
  as 
  an 
  

   indicator. 
  The 
  thiosulphate 
  solution 
  may 
  be 
  standardized 
  by 
  

   means 
  of 
  a 
  pure 
  cobalt 
  compound 
  or 
  by 
  means 
  of 
  potassium 
  

   dichromate. 
  In 
  the 
  latter 
  case, 
  as 
  the 
  cobalt 
  is 
  oxidized 
  to 
  the 
  

   trivalent 
  condition, 
  one 
  dichromate 
  is 
  equivalent 
  to 
  six 
  cobalts. 
  — 
  

   Jour. 
  Inclust. 
  and 
  Eng. 
  Chem., 
  viii, 
  No. 
  10. 
  h. 
  l. 
  w. 
  

  

  