﻿CLAYS 
  OF 
  Is'EW 
  YORK 
  521 
  

  

  action 
  on 
  the 
  clay, 
  by 
  the 
  formation 
  of 
  a 
  double 
  silicate 
  of 
  iron, 
  

   lime 
  and 
  alumina, 
  except 
  at 
  higher 
  temperatures. 
  

  

  Carbonate 
  of 
  lime 
  is 
  very 
  abundant 
  in 
  clays, 
  either 
  sedimentary 
  

   or 
  residual, 
  which 
  have 
  been 
  derived 
  from 
  areas 
  underlain 
  by 
  cal- 
  

   careous 
  rocks. 
  It 
  may 
  result 
  from 
  the 
  decomposition 
  of 
  lime-bear- 
  

   ing 
  feldspars. 
  Its 
  presence 
  as 
  carbonate 
  can 
  be 
  frequently 
  deter- 
  

   mined 
  by 
  treating 
  the 
  clay 
  with 
  muriatic 
  acid, 
  which 
  produces 
  

   efferv^escence 
  if 
  more 
  than 
  4^ 
  or 
  5^ 
  of 
  lime 
  carbonate 
  is 
  present. 
  

  

  The 
  effect 
  of 
  carbonate 
  of 
  lime 
  in 
  a 
  clay 
  depends 
  on 
  its 
  physical 
  

   condition. 
  If 
  present 
  in 
  the 
  form 
  of 
  lumps 
  or 
  pebbles, 
  it 
  is 
  very 
  

   injurious, 
  and 
  is 
  commonly 
  removed 
  by 
  screening 
  or 
  washing, 
  or 
  

   at 
  times 
  the 
  clay 
  is 
  simply 
  washed 
  to 
  break 
  up 
  the 
  lumps. 
  If 
  

   present 
  in 
  a 
  finely 
  divided 
  condition, 
  it 
  may 
  not 
  only 
  be 
  harmless 
  

   but 
  even 
  desirable, 
  provided 
  there 
  is 
  not 
  an 
  excess 
  of 
  it. 
  Clays 
  with 
  

   20^-25^ 
  of 
  carbonate 
  of 
  lime 
  can 
  be 
  used 
  for 
  common 
  or 
  even 
  

   pressed 
  bricks, 
  also 
  for 
  earthenware. 
  Calcareous 
  clays 
  find 
  an 
  ad- 
  

   ditional 
  use 
  in 
  the 
  manufacture 
  of 
  glazes. 
  

  

  The 
  effects 
  of 
  carbonate 
  of 
  lime 
  may 
  be 
  briefly 
  stated, 
  as 
  follows. 
  

   In 
  burning 
  the 
  lime 
  carbonate 
  is 
  broken 
  up 
  into 
  carbon 
  dioxid 
  and 
  

   caustic 
  lime. 
  If 
  the 
  clay 
  is 
  not 
  raised 
  to 
  the 
  temperature 
  of 
  

   ^^trification 
  in 
  order 
  to 
  make 
  the 
  lime 
  unite 
  by 
  fusion 
  with 
  other 
  

   ingredients, 
  the 
  lime 
  will 
  absorb 
  moisture 
  from 
  the 
  air 
  and 
  slake. 
  

   The 
  swelling 
  which 
  accompanies 
  this 
  may, 
  if 
  the 
  lime 
  is 
  in 
  lumps, 
  

   cause 
  a 
  bursting 
  or 
  flaking 
  of 
  the 
  brick. 
  

  

  Lime 
  also 
  tends 
  to 
  destroy 
  the 
  red 
  color, 
  produced 
  by 
  iron 
  in 
  

   burning, 
  giving 
  a 
  buff, 
  or 
  greenish 
  product, 
  depending 
  on 
  the 
  in- 
  

   tensity 
  of 
  the 
  firing. 
  To 
  destroy 
  the 
  iron 
  coloration, 
  it 
  is 
  necessary 
  

   for 
  the 
  clay 
  to 
  contain 
  threo 
  times 
  as 
  much 
  lime 
  as 
  iron. 
  Buff 
  

   colors 
  are 
  not 
  always 
  due 
  to 
  this 
  cause, 
  for 
  a 
  small 
  percentage 
  of 
  

   iron 
  in 
  a 
  clay 
  may 
  yield 
  the 
  same 
  hue. 
  

  

  In 
  high 
  grade 
  clays 
  large 
  amounts 
  of 
  lime 
  do 
  not 
  need 
  to 
  be 
  con- 
  

   sidered, 
  for 
  such 
  materials 
  can 
  not 
  be 
  used 
  ; 
  but 
  in 
  the 
  manufacture 
  

   of 
  building 
  brick, 
  pressed 
  brick, 
  or 
  terra 
  cotta, 
  it 
  is 
  sometimes 
  neces- 
  

   sary 
  to 
  use 
  clays 
  with 
  a 
  large 
  amount 
  of 
  lime, 
  either 
  from 
  necessity, 
  

  

  