﻿642 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  is 
  far 
  more 
  pronounced 
  in 
  the 
  case 
  of 
  buff 
  ware. 
  In 
  red 
  burning 
  

   clajs 
  the 
  effect 
  is 
  often 
  marked 
  by 
  a 
  superficial 
  reduction 
  of 
  the 
  

   iron 
  which 
  the 
  clay 
  contains^ 
  or 
  a 
  slagging 
  of 
  the 
  surface 
  due 
  to 
  the 
  

   deposition 
  of 
  fusible 
  impurities, 
  specially 
  alkalis, 
  from 
  the 
  fire 
  

   gases. 
  

  

  In 
  calcareous 
  clays 
  many 
  of 
  the 
  elements 
  of 
  the 
  material 
  show 
  

   a 
  strong 
  affinity 
  for 
  the 
  sulfuric 
  acid 
  of 
  the 
  fire 
  gas; 
  the 
  result 
  of 
  

   this 
  is 
  that 
  sulfate 
  of 
  lime 
  is 
  formed 
  on 
  the 
  surface, 
  and 
  the, 
  ferric 
  

   oxid, 
  not 
  being 
  able 
  to 
  unite 
  Avith 
  the 
  lime, 
  imparts 
  a 
  red 
  color 
  

   to 
  the 
  brick. 
  In 
  the 
  interior 
  the 
  color 
  of 
  the 
  brick 
  remains 
  yellow, 
  

   for 
  the 
  sulfuric 
  acid 
  gas 
  has 
  not 
  been 
  able 
  to 
  penetrate 
  to 
  that 
  point 
  

   and 
  take 
  the 
  lime 
  away 
  from 
  the 
  iron. 
  This 
  point 
  can 
  be 
  easily 
  

   proved 
  by 
  determining 
  the 
  amount 
  of 
  sulfur 
  in 
  the 
  yellow 
  and 
  the 
  

   red 
  portion 
  of 
  the 
  brick, 
  and, 
  if 
  the 
  theory 
  is 
  correct, 
  the 
  latter 
  

   should 
  show 
  the 
  greater 
  amount 
  of 
  the 
  acid. 
  That 
  this 
  is 
  so 
  id 
  

   well 
  shown 
  by 
  two 
  clays 
  analyses 
  made 
  by 
  Soger 
  (Ges. 
  8chrift. 
  p. 
  

   277). 
  The 
  outer 
  or 
  red 
  portion 
  of 
  the 
  brick 
  which 
  he 
  analyzed 
  

   showed 
  14.43^ 
  of 
  sulfuric 
  acid, 
  while 
  the 
  inner 
  or 
  yellow 
  portion 
  

   showed 
  only 
  1,04^. 
  

  

  One 
  fact 
  that 
  this 
  emphasizes 
  is 
  that 
  in 
  burning 
  calcareous 
  clays 
  

   it 
  is 
  important 
  that 
  coal 
  should 
  be 
  used 
  which 
  contains 
  but 
  a 
  very 
  

   small 
  percentage 
  of 
  sulfur. 
  

  

  The 
  slower 
  the 
  burning 
  proceeds, 
  the 
  more 
  completely 
  will 
  the 
  

   iron 
  in 
  all 
  portions 
  of 
  the 
  clay 
  be 
  oxidized, 
  and 
  the 
  greater 
  the 
  ac- 
  

   cess 
  of 
  air 
  the 
  brighter 
  will 
  be 
  the 
  red 
  color. 
  

  

  The 
  time 
  required 
  in 
  drying 
  and 
  burning 
  is 
  affected 
  not 
  only 
  by 
  

   the 
  clay, 
  but 
  also 
  by 
  the 
  process. 
  The 
  more 
  water 
  which 
  has 
  to 
  be 
  

   driven 
  off 
  in 
  the 
  kiln, 
  the 
  slower 
  must 
  the 
  burning 
  proceed, 
  unless 
  

   the 
  clay 
  is 
  coarse-grained. 
  

  

  