﻿CLAYS 
  OF 
  XEW 
  YORK 
  571 
  

  

  Brick 
  clays 
  often 
  have 
  more 
  or 
  less 
  organic 
  matter 
  which 
  may 
  

   sometimes 
  reduce 
  the 
  iron. 
  Thus 
  the 
  clay 
  from 
  Rathenow, 
  when 
  

   ignited 
  in 
  a 
  closed 
  crucible, 
  showed 
  2.20^ 
  of 
  ferrous 
  oxid. 
  In 
  

   the 
  presence 
  of 
  air, 
  however, 
  it 
  was 
  converted 
  to 
  ferric 
  oxid, 
  for 
  

   after 
  being 
  ignited 
  for 
  one 
  hour, 
  exposed 
  to 
  the 
  air, 
  the 
  same 
  clay 
  

   showed 
  only 
  .76^ 
  of 
  ferrous 
  oxid. 
  

  

  The 
  black 
  color 
  of 
  bricks 
  is 
  due 
  to 
  the 
  reduction 
  of 
  iron 
  in 
  the 
  

   last 
  stages 
  of 
  burning. 
  

  

  One 
  interesting 
  result 
  of 
  Seger's 
  experiments 
  is 
  that 
  oxidation 
  

   of 
  the 
  iron 
  can 
  take 
  pla.ce 
  within 
  a 
  clay 
  which 
  has 
  been 
  burned 
  

   t.i 
  vitrification. 
  This 
  was 
  explained 
  by 
  an 
  experiment 
  in 
  which 
  

   he 
  took 
  a 
  prism 
  2 
  cm 
  thick, 
  and 
  burned 
  it 
  to 
  vitrification. 
  After 
  

   burning, 
  the 
  surface 
  of 
  the 
  prism 
  was 
  cherry 
  red, 
  but 
  in 
  passing 
  

   from 
  the 
  middle 
  to 
  the 
  surface 
  the 
  colors 
  encountered 
  were 
  cherry 
  

   red, 
  gray 
  red, 
  gray 
  green, 
  black 
  violet, 
  gray 
  green, 
  gray 
  red, 
  and 
  

   cherry 
  red. 
  An 
  analysis 
  of 
  these 
  different 
  colored 
  portions 
  showed 
  

   the 
  following: 
  

  

  Cherry 
  red 
  Gray 
  green 
  Black 
  violet 
  

  

  Ferric 
  oxid 
  5.35 
  3.43 
  :i.l4 
  

  

  Ferrous 
  oxid 
  .12 
  1 
  . 
  85 
  3.01 
  

  

  The 
  above 
  is 
  explained 
  by 
  supposing 
  that 
  the 
  flame 
  of 
  the 
  fire 
  

   caused 
  a 
  reducing 
  action 
  of 
  the 
  iron, 
  which 
  did 
  not 
  extend 
  the 
  

   entire 
  distance 
  to 
  the 
  core 
  ; 
  later, 
  on 
  cooling 
  the 
  outer 
  portion 
  of 
  

   the 
  brick 
  was 
  reoxidized. 
  

  

  