﻿534 
  KEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  3 
  The 
  color 
  to 
  whicli 
  the 
  clay 
  burns. 
  This 
  may 
  also 
  be 
  judged 
  

   approximately, 
  for 
  the 
  greater 
  the 
  amount 
  of 
  iron 
  present 
  the 
  deeper 
  

   red 
  will 
  the 
  clay 
  burn, 
  provided 
  the 
  iron 
  is 
  evenly 
  and 
  finely 
  dis- 
  

   tributed 
  and 
  an 
  excess 
  of 
  lime 
  is 
  not 
  contained 
  in 
  the 
  clay. 
  If 
  the 
  

   proportion 
  of 
  iron 
  tO' 
  lime 
  is 
  as 
  1 
  tO' 
  3, 
  then 
  a 
  buff 
  product 
  results, 
  

   provided 
  the 
  clay 
  is 
  heated 
  to 
  incipient 
  fusion 
  or 
  vitrification. 
  The 
  

   above 
  conditions 
  will 
  be 
  affected 
  by 
  a 
  reducing 
  atmosphere 
  in 
  burn- 
  

   ing 
  or 
  the 
  presence 
  of 
  sulfur 
  in 
  the 
  fire 
  gases. 
  

  

  4 
  The 
  quantity 
  of 
  combined 
  water. 
  Clays 
  with 
  a 
  large 
  amount 
  

   of 
  combined 
  water 
  sometimes 
  exhibit 
  a, 
  tendency 
  tO' 
  crack 
  in 
  burn- 
  

   ing. 
  This 
  combined 
  water 
  would 
  be 
  shown 
  in 
  the 
  chemical 
  

   analysis. 
  

  

  6 
  Excess 
  of 
  silica. 
  A 
  large 
  excess 
  of 
  silica 
  would 
  indicate 
  a 
  sandy 
  

   clay. 
  

  

  These 
  are 
  practically 
  all 
  the 
  points 
  which 
  the 
  ultimate 
  analysis 
  

   explains, 
  and 
  they 
  are 
  mostly 
  of 
  a 
  chemical 
  nature. 
  As 
  regards 
  the 
  

   rational 
  analysis, 
  it 
  may 
  be 
  carried 
  out 
  in 
  a 
  simple 
  way 
  or 
  an 
  

   elaborate 
  one. 
  

  

  Most 
  kaolins 
  and 
  other 
  high 
  grade 
  clays 
  consist 
  only 
  of 
  kaolinite, 
  

   quartz 
  and 
  feldspar, 
  the 
  kaolinite 
  forming 
  the 
  finest 
  particles 
  of 
  

   the 
  mass, 
  while 
  the 
  balance 
  is 
  quartz, 
  feldspar, 
  and 
  perhaps 
  some 
  

   mica. 
  The 
  finest 
  particles 
  are 
  known 
  as 
  the 
  clay 
  substance, 
  which 
  

   may 
  be 
  looked 
  on 
  as 
  having 
  the 
  properties 
  of 
  kaolinite, 
  for 
  the 
  

   latter 
  is 
  present 
  in 
  it 
  in 
  such 
  a 
  large 
  excess. 
  'Now 
  as 
  each 
  of 
  these 
  

   three 
  components 
  of 
  the 
  kaolin 
  — 
  clay 
  substance, 
  quartz 
  and 
  feld- 
  

   spar 
  — 
  have 
  characteristic 
  properties, 
  the 
  kaolin 
  will 
  vary 
  in 
  its 
  

   behavior 
  according 
  as 
  one 
  or 
  the 
  other 
  of 
  these 
  constituents 
  pre- 
  

   dominates 
  or 
  tends 
  to 
  increase. 
  

  

  As 
  to 
  the 
  characters 
  of 
  these 
  three. 
  Quartz 
  is 
  nearly 
  infusible, 
  

   nonplastic, 
  has 
  very 
  little 
  shrinkage, 
  and 
  is 
  of 
  low 
  tensile 
  strength; 
  

   feldspar 
  is 
  easily 
  fusible 
  and 
  of 
  low 
  plasticity 
  by 
  itself; 
  kaolinite 
  is 
  

   plastic 
  and 
  quite 
  refractor)^, 
  but 
  shrinks 
  considerably 
  in 
  burning. 
  

  

  In 
  Europe, 
  specially 
  Germany, 
  the 
  custom 
  has 
  been 
  to 
  disregard 
  

   mica 
  and 
  figure 
  it 
  in 
  as 
  clay 
  substance, 
  partly 
  because 
  there 
  was 
  so 
  

  

  