﻿CLAYS 
  OF 
  NEW 
  YORK 
  681 
  

  

  fore 
  according 
  to 
  Dr 
  Gerlach 
  the 
  main 
  cause 
  of 
  sulfates, 
  which 
  

   give 
  rise 
  to 
  " 
  white 
  wash 
  ". 
  Sulfates 
  may 
  also 
  come 
  from 
  the 
  sulfur 
  

   contained 
  in 
  the 
  water 
  used 
  in 
  the 
  tempering 
  of 
  the 
  clay, 
  such 
  

   waters 
  often 
  containing 
  gypsum, 
  and, 
  as 
  many 
  clays 
  often 
  require 
  

   30^ 
  or 
  perhaps 
  more 
  of 
  water 
  to 
  render 
  them 
  plastic, 
  it 
  is 
  easily 
  

   seen 
  that 
  the 
  clay 
  may 
  receive 
  a 
  large 
  addition 
  of 
  lime 
  sulfate. 
  

   This 
  sulfate 
  might 
  be 
  present 
  in 
  the 
  mineral 
  coloring 
  matter 
  added 
  

   to 
  the 
  bricks. 
  Rapid 
  drying 
  causes 
  the 
  water 
  to 
  evaporate 
  more 
  

   quickly 
  and 
  a 
  lesser 
  amount 
  of 
  the 
  dissolved 
  sulfates 
  is 
  apt 
  to 
  be 
  

   brought 
  to 
  the 
  surface 
  of 
  the 
  ware. 
  

  

  2 
  Sulfates 
  arising 
  during 
  water-smoking 
  and 
  burning. 
  In 
  the 
  

  

  water-smoking 
  of 
  a 
  kiln 
  those 
  bricks 
  nearest 
  the 
  fireplaces 
  will 
  lose 
  

   their 
  moisture 
  first, 
  and 
  before 
  the 
  bricks 
  farthest 
  from 
  the 
  fireplace 
  

   are 
  heated 
  to 
  a 
  temperature 
  sufficient 
  to 
  convent 
  their 
  moisture 
  into 
  

   steam; 
  therefore 
  much 
  of 
  the 
  watery 
  vapor 
  driven 
  off 
  from 
  the 
  

   bricks 
  which 
  were 
  heated 
  first 
  will 
  be 
  deposited 
  on 
  the 
  surface 
  of 
  

   those 
  farthest 
  from 
  the 
  fireplace, 
  and 
  be 
  absorbed 
  by 
  them 
  to 
  a 
  

   certain 
  extent. 
  If 
  it 
  happens 
  that 
  these 
  green 
  bricks 
  contain 
  soluble 
  

   sulfates, 
  the 
  deposition 
  of 
  this 
  condensed 
  vapor 
  on 
  them 
  will 
  tend 
  to 
  

   increase 
  the 
  sulfates 
  in 
  solution, 
  and 
  when 
  their 
  water 
  is 
  driven 
  off 
  

   all 
  the 
  sulfates 
  will 
  be 
  canied 
  to 
  the 
  surface 
  in 
  solution 
  and 
  de- 
  

   posited 
  there. 
  This 
  condensation 
  of 
  the 
  waiter 
  will 
  be 
  harmless, 
  if 
  

   the 
  clay 
  contains 
  no 
  soluble 
  sulfates 
  or 
  if 
  the 
  contained 
  soluble 
  

   sulfates 
  have 
  been 
  previously 
  rendered 
  insoluble 
  by 
  the 
  addition 
  of 
  

   the 
  proper 
  chemicals. 
  Another 
  source 
  of 
  difficulty 
  may 
  come 
  from 
  

   the 
  use 
  of 
  sulfurous 
  fuel, 
  for 
  it 
  is 
  known 
  that 
  many 
  coals 
  contain 
  

   more 
  or 
  less 
  iron 
  pyriite. 
  This 
  sulfurous 
  acid 
  gas 
  in 
  passing 
  through 
  

   the 
  kiln 
  wiU 
  only 
  too 
  willingly 
  attack 
  carbonates 
  present 
  in 
  the 
  clay 
  

   and 
  form 
  sulfurous 
  salts, 
  which 
  as 
  the 
  heat 
  of 
  the 
  kiln 
  increases, 
  

   come 
  to 
  the 
  surface, 
  and 
  are 
  there 
  oxidized 
  to 
  sulfuric 
  salts 
  or 
  sul- 
  

   fates, 
  these 
  causing 
  efflorescence 
  or 
  discoloration. 
  

  

  Efflorescences 
  formed 
  on 
  burned 
  ware. 
  It 
  not 
  infrequently 
  hap- 
  

   pens 
  that 
  clay 
  products 
  come 
  from 
  the 
  kiln 
  apparently 
  free 
  from 
  

   any 
  superficial 
  discoloration 
  and 
  later 
  develop 
  one 
  when 
  subjected 
  

  

  