﻿336 
  Posnjak 
  and 
  Merwin 
  — 
  Hydrated 
  Ferric 
  Oxides. 
  

  

  As 
  seen 
  in 
  the 
  table 
  (Table 
  VII), 
  lepidocrocite 
  has 
  a 
  con- 
  

   siderably 
  lower 
  specific 
  gravity 
  than 
  goethite. 
  The 
  value 
  

   4-07 
  derived 
  from 
  No. 
  11 
  is 
  probably 
  the 
  better 
  value 
  of 
  

   the 
  two 
  given, 
  since 
  the 
  substance 
  was 
  purer. 
  The 
  wide 
  

   variation 
  and 
  difference 
  of 
  the 
  observed 
  specific 
  gravities 
  

   of 
  goethite 
  and 
  the 
  "limonites" 
  have 
  practically 
  disap- 
  

   peared, 
  but 
  the 
  corrected 
  values 
  of 
  the 
  "limonites'' 
  are 
  

   now 
  slightly 
  higher 
  than 
  the 
  value 
  for 
  goethite. 
  How- 
  

   ever, 
  it 
  would 
  not 
  be 
  safe 
  to 
  place 
  much 
  reliance 
  on 
  that 
  

   difference 
  as 
  the 
  corrections 
  applied 
  to 
  most 
  "limonites" 
  

   are 
  very 
  large 
  (about 
  six 
  times 
  that 
  difference). 
  The 
  

   assumed 
  mineral 
  compositions 
  are 
  also 
  somewhat 
  uncer- 
  

   tain 
  and 
  the 
  correction 
  may 
  therefore 
  not 
  be 
  exact. 
  It 
  

   would 
  be 
  preferable 
  for 
  that 
  reason 
  to 
  consider 
  that 
  the 
  

   observed 
  difference 
  in 
  the 
  corrected 
  values 
  of 
  goethite 
  

   and 
  '^imonites'' 
  is 
  caused 
  by 
  such 
  errors 
  and, 
  as 
  long 
  

   as 
  there 
  is 
  no 
  other 
  evidence 
  in 
  favor 
  of 
  their 
  polymor- 
  

   phy, 
  to 
  assume 
  that 
  they 
  are 
  identical. 
  The 
  optical 
  study 
  

   furnishes 
  much 
  in 
  favor 
  of 
  that 
  assumption 
  (see 
  Table 
  

   IV). 
  

  

  Specific 
  Gravity 
  of 
  Turgite. 
  — 
  It 
  will 
  be 
  remembered 
  

   that 
  the 
  dehydration 
  experiments 
  indicated 
  that 
  turgite, 
  

   on 
  account 
  of 
  the 
  gradual 
  loss 
  of 
  water 
  on 
  heating, 
  could 
  

   not 
  be 
  a 
  definite 
  chemical 
  compound. 
  Analysis 
  and 
  opti- 
  

   cal 
  observation 
  showed 
  the 
  variability 
  of 
  this 
  substance 
  

   and 
  thus 
  supported 
  this 
  conclusion. 
  These 
  facts 
  led 
  to 
  

   the 
  view 
  that 
  the 
  water 
  in 
  turgite 
  must 
  either 
  be 
  adsorbed 
  

   or 
  dissolved. 
  Rehydration 
  experiments, 
  however, 
  indi- 
  

   cated 
  that 
  this 
  water 
  in 
  all 
  probability 
  was 
  mostly 
  not 
  

   adsorbed, 
  and 
  this 
  finds 
  further 
  support 
  in 
  specific 
  grav- 
  

   ity 
  determinations 
  of 
  turgite. 
  These 
  are 
  given 
  in 
  Table 
  

   VIII. 
  The 
  values 
  corrected 
  for 
  the 
  small 
  amounts 
  of 
  

   silica 
  and 
  ferrous 
  carbonate 
  are 
  also 
  given, 
  as 
  well 
  as 
  the 
  

   corresponding 
  specific 
  volumes. 
  

  

  

  

  Table 
  VIII. 
  

  

  

  

  No. 
  

   (Tab. 
  I) 
  

  

  •, 
  no 
  

  

  Sp. 
  gr. 
  Sp. 
  gr. 
  cor- 
  

   mineral 
  25° 
  rected 
  for 
  

   water 
  25° 
  SiO. 
  and 
  FeCO, 
  

  

  Sp. 
  % 
  hem- 
  

   volume 
  atite 
  

  

  %goeth 
  

   ite 
  

  

  1 
  

   2 
  

   3 
  

  

  1-30 
  

   412 
  

   4-68 
  

  

  4-978 
  5050 
  

   4-607 
  4-648 
  

   4-670 
  4-730 
  

  

  0-198 
  87 
  

   0-215 
  59 
  

   0-211 
  53 
  

  

  13 
  

  

  41 
  

   47 
  

  

  If 
  the 
  water 
  is 
  adsorbed 
  the 
  specific 
  volume 
  of 
  turgite 
  

   should 
  be 
  very 
  nearly 
  the 
  sum 
  of 
  the 
  specific 
  volumes 
  of 
  

  

  