﻿CLAYS 
  OF 
  KEW 
  YOEK 
  515 
  

  

  is 
  imperYious 
  or 
  nearly 
  so, 
  tlie 
  alkalis 
  are 
  added 
  for 
  fiuxiug 
  to 
  the 
  

   body 
  in 
  tlie 
  form 
  of 
  feldspar. 
  Much 
  feldspar 
  is 
  mined 
  both 
  in 
  the 
  

   United 
  States 
  and 
  Europe 
  for 
  pottei^' 
  use, 
  but 
  in 
  nearly 
  every 
  case 
  

   it 
  is 
  the 
  potash 
  feldspar. 
  

  

  Alkalis 
  exert 
  little 
  or 
  no 
  coloring 
  influence 
  on 
  the 
  burned 
  ware 
  

   in 
  most 
  instances, 
  but 
  if 
  an 
  excess 
  of 
  feldspar 
  be 
  added 
  to 
  a 
  white 
  

   burning 
  clay, 
  it 
  will 
  produce 
  a 
  creamy 
  tint 
  when 
  burned. 
  Potash 
  

   seems 
  to 
  have 
  a 
  tendency- 
  to 
  deepen 
  the 
  color 
  of 
  a 
  ferruginous 
  clay 
  

   in 
  burning. 
  

  

  The 
  amount 
  of 
  alkalis 
  contained 
  in 
  clay 
  varies. 
  It 
  may 
  sink 
  to 
  

   a 
  mere 
  trace 
  or 
  rise 
  to 
  7^ 
  or 
  8^. 
  The 
  limits 
  for 
  a 
  number 
  of 
  clays 
  

   are 
  given 
  below 
  the 
  figures 
  being 
  taken 
  from 
  tables 
  at 
  end 
  of 
  report. 
  

  

  Rauge 
  Aver. 
  

  

  Kaolins 
  10^6.21 
  1.01 
  

  

  Fire 
  clays 
  048-5.27 
  1.46 
  

  

  Pottery 
  clays 
  52-7 
  .11 
  2.06 
  

  

  Brick 
  clays 
  17-15 
  .32 
  2 
  . 
  768 
  

  

  Iron 
  ox 
  id 
  

  

  Iron 
  oxid 
  is 
  the 
  gi'eat 
  coloring 
  agent 
  of 
  both 
  burned 
  and 
  un- 
  

   bumed 
  clay, 
  and 
  in 
  addition 
  ser^^es 
  as 
  a 
  flux. 
  Furthermore 
  in 
  the 
  

   form 
  of 
  hydrated 
  oxid 
  it 
  may 
  increase 
  the 
  absorptive 
  power 
  of 
  

   clay.^ 
  

  

  It 
  is 
  not 
  only 
  one 
  of 
  the 
  most 
  widespread 
  and 
  common 
  of 
  clay 
  

   ingredients, 
  but 
  is 
  also 
  derived 
  fro^m 
  the 
  greatest 
  number 
  of 
  

   minerals. 
  The 
  compounds 
  which 
  may 
  serve 
  as 
  sources 
  of 
  iron 
  oxid 
  

   in 
  clays 
  are 
  

  

  Oxids 
  — 
  • 
  limonite, 
  hematite, 
  magTietite, 
  ilmenite 
  

  

  Silicates 
  — 
  mica, 
  hornblende, 
  garnet, 
  etc. 
  

  

  Sulfids 
  — 
  pyrite, 
  marcasite 
  

  

  Sulfates 
  — 
  melanterite 
  

  

  Carbonates 
  — 
  siderite 
  

  

  ^ 
  E. 
  A. 
  Smith. 
  Ala. 
  geol. 
  sur., 
  rep't 
  on 
  agricult. 
  p. 
  45. 
  

  

  