﻿328 
  Posnjak 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  

  

  curve 
  (extended 
  considerably 
  beyond 
  the 
  decomposition 
  

   temperature) 
  together 
  with 
  exact 
  analytical 
  data, 
  should 
  

   give 
  definite 
  information 
  about 
  the 
  nature 
  of 
  the 
  sub- 
  

   stance 
  in 
  question. 
  

  

  The 
  hydration 
  experiments 
  were 
  carried 
  out 
  at 
  as 
  slow 
  

   a 
  rate 
  as 
  practicable 
  and 
  the 
  heating 
  at 
  all 
  the 
  tempera- 
  

   tures 
  required 
  over 
  four 
  months. 
  The 
  substance 
  was 
  

   ground, 
  placed 
  in 
  a 
  small 
  weighing 
  glass 
  and 
  heated 
  in 
  an 
  

   electric 
  furnace 
  which 
  was 
  kept 
  constant 
  within 
  ±5°. 
  A 
  

   slow 
  stream 
  of 
  air, 
  dried 
  over 
  sulphuric 
  acid, 
  was 
  passed 
  

   through 
  the 
  furnace. 
  For 
  weighing, 
  the 
  substance 
  was 
  

   quickly 
  placed 
  in 
  a 
  desiccator 
  over 
  sulphuric 
  acid 
  and, 
  

   when 
  sufficiently 
  cooled, 
  was 
  covered 
  and 
  weighed. 
  

   Before 
  putting 
  it 
  back 
  in 
  the 
  furnace 
  the 
  substance 
  was 
  

   slightly 
  shaken 
  up. 
  At 
  least 
  twenty-four 
  hours 
  elapsed 
  

   between 
  successive 
  weighings 
  and 
  the 
  substance 
  was 
  

   treated 
  at 
  a 
  different 
  temperature 
  only 
  if 
  no 
  change 
  

   occurred 
  after 
  two 
  more 
  days 
  heating. 
  

  

  Most 
  of 
  the 
  time 
  required 
  by 
  the 
  dehydration 
  experi- 
  

   ments 
  was 
  consumed 
  for 
  the 
  decomposition 
  of 
  the 
  sub- 
  

   stance. 
  Before 
  decomposition 
  begins 
  and 
  after 
  it 
  is 
  

   practically 
  completed, 
  the 
  substance 
  comes 
  very 
  rapidly 
  

   to 
  constancy 
  under 
  the 
  conditions 
  of 
  experiment. 
  Decom- 
  

   position 
  proceeds, 
  however, 
  at 
  an 
  exceedingly 
  slow 
  rate 
  

   at 
  the 
  temperature 
  at 
  which 
  it 
  is 
  first 
  discovered 
  and 
  it 
  

   was 
  necessary 
  to 
  raise 
  the 
  temperature 
  considerably 
  to 
  

   dehydrate 
  the 
  substance 
  within 
  a 
  reasonable 
  period. 
  

  

  The 
  results 
  of 
  the 
  dehydration 
  experiments 
  are 
  given 
  in 
  

   figs. 
  3 
  and 
  4. 
  With 
  the 
  exception 
  of 
  turgite, 
  all 
  the 
  

   hydrated 
  ferric 
  oxides 
  examined 
  show 
  similar 
  dehydra- 
  

   tion 
  curves 
  which 
  consist 
  of 
  three 
  distinct 
  parts. 
  The 
  

   decomposition 
  of 
  the 
  substance 
  takes 
  place 
  in 
  the 
  middle 
  

   portion 
  of 
  the 
  curve 
  and 
  is 
  accompanied 
  by 
  the 
  color 
  

   change 
  from 
  yellow 
  to 
  red. 
  It 
  should 
  probably 
  take 
  place 
  

   at 
  a 
  single 
  temperature, 
  but 
  owing 
  to 
  the 
  practical 
  irre- 
  

   versibility 
  of 
  the 
  reaction 
  and 
  its 
  slowness 
  this 
  tempera- 
  

   ture 
  can 
  not 
  be 
  fixed 
  and 
  decomposition 
  therefore 
  is 
  

   determined 
  within 
  the 
  temperature 
  interval 
  between 
  the 
  

   point 
  at 
  which 
  continuous 
  loss 
  was 
  first 
  observed 
  and 
  the 
  

   somewhat 
  higher 
  temperature 
  at 
  which 
  for 
  practical 
  rea- 
  

   sons 
  the 
  dehydration 
  was 
  carried 
  out. 
  87 
  

  

  37 
  In 
  the 
  drawings 
  this 
  interval 
  is 
  indicated 
  by 
  the 
  broken 
  line. 
  The 
  line 
  

   connecting 
  the 
  upper 
  and 
  lower 
  portion 
  of 
  the 
  curves 
  is 
  drawn 
  at 
  the 
  point 
  

   at 
  which 
  continuous 
  loss 
  of 
  water 
  was 
  observed, 
  which 
  however 
  does 
  not 
  

   represent 
  the 
  exact 
  decomposition 
  temperature. 
  

  

  