﻿CLAYS 
  OF 
  NEW 
  YOEK 
  517 
  

  

  matter, 
  and 
  this 
  material, 
  if 
  present 
  in 
  a 
  dense 
  wet 
  clay, 
  tO' 
  which 
  

   the 
  air 
  can 
  not 
  gain 
  access, 
  may 
  keep 
  the 
  iron 
  in 
  a 
  ferrous 
  condition. 
  

  

  Whenever 
  the 
  iron 
  exists 
  in 
  the 
  clay 
  in 
  combination 
  with 
  silica, 
  

   it 
  is 
  present 
  probably 
  as 
  a 
  complex 
  silicate, 
  for 
  pnre 
  ferric 
  silicate 
  is 
  

   veiy 
  rare 
  in 
  nature. 
  

  

  The 
  presence 
  of 
  ferric 
  hydrate 
  in 
  clay 
  increases 
  its 
  absorptive 
  

   power 
  for 
  both 
  gases 
  and 
  water, 
  but 
  both 
  it 
  and 
  the 
  carbonate 
  are 
  

   converted 
  in 
  burning 
  to 
  the 
  oxid. 
  

  

  While 
  it 
  may 
  be 
  said 
  that 
  the 
  burning 
  of 
  clay 
  in 
  an 
  oxidizing 
  

   fire 
  converts 
  the 
  iron 
  to 
  the 
  condition 
  of 
  ferric 
  oxid, 
  still 
  this 
  state- 
  

   ment 
  only 
  holds 
  true 
  up 
  to 
  a 
  certain 
  temperature, 
  depending 
  on 
  the 
  

   fusibility 
  of 
  the 
  clay, 
  for 
  in 
  every 
  clay 
  the 
  iron 
  see:ms 
  to 
  return 
  to 
  

   the 
  ferrous 
  condition 
  as 
  the 
  point 
  of 
  vitrification 
  is 
  approached. 
  

   The 
  change 
  would 
  of 
  course 
  be 
  accompanied 
  by 
  a 
  liberation 
  of 
  

   oxygen, 
  which 
  would 
  increase 
  with 
  the 
  amount 
  of 
  iron 
  in 
  the 
  clay, 
  

   and 
  may 
  account 
  for 
  the 
  greater 
  blistering 
  of 
  ferruginous 
  clays 
  as 
  

   the 
  point 
  of 
  vitrification 
  is 
  passed, 
  and 
  that 
  of 
  viscosity 
  approached. 
  

  

  While 
  this 
  fact 
  is 
  not 
  unknovm, 
  very 
  little 
  attention 
  seems 
  to 
  

   have 
  been 
  paid 
  to 
  it. 
  

  

  E-emole 
  ^ 
  considers 
  that 
  the 
  greenish 
  color 
  of 
  hard 
  burned 
  clays 
  

   is 
  due 
  to 
  this 
  cause. 
  Seger^ 
  also 
  notes 
  the 
  ferrous 
  condition 
  of 
  

   iron 
  at 
  high 
  temperatures, 
  and 
  states 
  that 
  in 
  this 
  form 
  it 
  is 
  a 
  

   powerful 
  flux. 
  

  

  The 
  tendency 
  of 
  iron 
  oxid 
  is 
  to 
  unite 
  mth 
  the 
  silica 
  and 
  alumina 
  

   and 
  also 
  with 
  the 
  lime 
  of 
  the 
  clay 
  the 
  moment 
  that 
  fusion 
  begins, 
  

   thereby 
  fomiing 
  a 
  complex 
  silicate, 
  whose 
  fusibility 
  is 
  lower 
  than 
  

   the 
  simpler 
  ones 
  from 
  whose 
  union 
  it 
  was 
  formed. 
  

  

  The 
  experiments 
  of 
  Berthier 
  (Percy's 
  Metallurgy, 
  refractory 
  

   materials 
  and 
  fuel, 
  p. 
  60-75) 
  on 
  mixtures 
  of 
  iron, 
  alumina 
  and 
  

   silica 
  point 
  out 
  these 
  facts 
  very 
  clearly. 
  These 
  consisted 
  in 
  making 
  

   up 
  the 
  mixtures 
  given 
  below 
  and 
  subjecting 
  them 
  to 
  a 
  high 
  tem- 
  

   perature, 
  that 
  of 
  molten 
  steel, 
  with 
  the 
  results 
  also 
  stated 
  below. 
  

  

  ^ 
  Wagner. 
  Manual 
  of 
  chemical 
  technology. 
  1897. 
  p. 
  634. 
  

   «Seger. 
  G^s. 
  Schrift. 
  \k 
  o91. 
  

  

  