﻿562 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  character 
  of 
  the 
  clay, 
  though 
  the 
  primary 
  changes 
  are 
  of 
  a 
  chemi- 
  

   cal 
  nature. 
  In 
  kaolins 
  this 
  change 
  simply 
  amounts 
  to 
  the 
  loss 
  

   by 
  the 
  kaolinite 
  or 
  clay 
  substance 
  of 
  its 
  combined 
  water. 
  In 
  

   impure 
  clays 
  many 
  other 
  changes 
  may 
  occur, 
  viz: 
  

  

  The 
  burning 
  off 
  of 
  organic 
  matter. 
  

  

  Limonite 
  losing 
  its 
  water 
  and 
  becoming 
  hematite. 
  

  

  Fyrite 
  (FeS^) 
  becoming 
  oxidized 
  to 
  ferric 
  sulfates, 
  which 
  in 
  

   turn 
  are 
  broken 
  up 
  by 
  the 
  expulsion 
  of 
  their 
  sulfur, 
  leaving 
  hema- 
  

   tite 
  or 
  ferric 
  oxid. 
  Both 
  lime 
  and 
  magnesium 
  carbonates 
  if 
  pres- 
  

   ent 
  will 
  part 
  with 
  their 
  carbon 
  dioxid. 
  

  

  The 
  general 
  effect 
  of 
  these 
  changes 
  is 
  first 
  to 
  make 
  the 
  clay 
  more 
  

   porous, 
  but 
  subsequently 
  to 
  increase 
  its 
  shrinkage. 
  The 
  color 
  of 
  

   the 
  clay 
  is 
  also 
  changed. 
  A 
  chemical 
  interaction 
  between 
  the 
  com- 
  

   ponent 
  minerals 
  of 
  the 
  clay 
  has 
  not 
  taken 
  place 
  up 
  to 
  this, 
  point. 
  

  

  It 
  is 
  held 
  by 
  Seger^ 
  that 
  the 
  more 
  plastic 
  a 
  clay 
  is 
  when 
  wet, 
  the 
  

   harder 
  it 
  will 
  be 
  after 
  light 
  burning. 
  Such 
  lightly 
  burned 
  wares 
  

   will 
  not, 
  however, 
  withstand 
  weathering 
  or 
  pressure, 
  and 
  are 
  very 
  

   porous; 
  resistance 
  to 
  weathering 
  is 
  attained 
  only 
  when 
  certain 
  por- 
  

   tions 
  of 
  the 
  clay 
  fuse, 
  and 
  unite 
  the 
  whole 
  into 
  a 
  stony 
  mass. 
  

  

  The 
  shrinkage 
  and 
  decrease 
  in 
  porosity 
  will 
  be 
  the 
  greater, 
  the 
  

   larger 
  the 
  number 
  of 
  particles 
  taking 
  part 
  in 
  the 
  fusion 
  of 
  the 
  

   mass. 
  

  

  The 
  process 
  of 
  fusion 
  involves 
  two 
  separate 
  processes, 
  one 
  physi- 
  

   cal, 
  causing 
  change 
  in 
  volume, 
  and 
  one 
  chemical, 
  giving 
  rise 
  to 
  the 
  

   formation 
  of 
  new 
  compounds 
  in 
  the 
  mass. 
  These 
  have 
  a 
  lower 
  

   fusing 
  point 
  than 
  the 
  substances 
  through 
  whose 
  interaction 
  they 
  

   were 
  formed. 
  In 
  some 
  cases 
  however 
  it 
  is 
  probable 
  that 
  solution 
  

   takes 
  place. 
  

  

  From 
  the 
  foregoing 
  it 
  would 
  appear 
  that 
  the 
  fusion 
  of 
  a 
  clay 
  

   is 
  influenced 
  not 
  only 
  by 
  the 
  melting 
  point 
  of 
  the 
  most 
  easily 
  fusible 
  

   component 
  of 
  the 
  clay, 
  but 
  also 
  by 
  the 
  relative 
  amount 
  of 
  infusible 
  

   ingredients, 
  and 
  the 
  relative 
  size 
  of 
  the 
  fluxing 
  and 
  nonfluxing 
  

   particles. 
  In 
  the 
  earlier 
  stages 
  of 
  fusion 
  we 
  must 
  therefore 
  look 
  

  

  1 
  Seger. 
  Oes. 
  Schrift. 
  p. 
  380. 
  

  

  