﻿270 
  Geological 
  Survey 
  of 
  Louisiana 
  [Sect. 
  

  

  been 
  found 
  that 
  if 
  the 
  clay 
  contains 
  a 
  large 
  percentage 
  of 
  

   alumina, 
  that 
  the 
  coloration 
  produced 
  by 
  the 
  iron 
  will 
  be 
  much 
  

   fainter 
  than 
  if 
  the 
  percentage 
  of 
  alumina 
  were 
  smaller. 
  Lime, 
  

   however, 
  is 
  far 
  more 
  powerful 
  in 
  this 
  respect 
  than 
  alumina, 
  for 
  

   if 
  the 
  lime 
  percentage 
  is 
  only 
  one 
  and 
  one-half 
  times 
  greater 
  

   than 
  that 
  of 
  the 
  iron 
  it 
  begins 
  to 
  exert 
  a 
  bleaching 
  action 
  on 
  the 
  

   color 
  of 
  the 
  clay 
  in 
  burning, 
  and 
  if 
  the 
  ratio 
  of 
  lime 
  to 
  iron 
  is 
  

   as 
  three 
  to 
  one 
  the 
  brick 
  instead 
  of 
  burning 
  red 
  will 
  burn 
  buff. 
  

   This 
  explains 
  the 
  cream 
  color 
  of 
  many 
  cream 
  colored 
  bricks. 
  

   It 
  should 
  be 
  added, 
  however, 
  that 
  a 
  small 
  percentage 
  of 
  iron 
  in 
  a 
  

   clay 
  will 
  produce 
  the 
  same 
  shade, 
  but 
  the 
  limy 
  clay 
  will 
  not 
  

   stand 
  much 
  heat 
  whereas 
  the 
  one 
  low 
  in 
  iron 
  will, 
  and 
  further- 
  

   more 
  if 
  they 
  are 
  overburned, 
  the 
  limy 
  one 
  will 
  turn 
  green- 
  

   ish 
  yellow, 
  and 
  the 
  other 
  will 
  tend 
  to 
  pass 
  into 
  a 
  deep 
  buff 
  or 
  

   deep 
  red. 
  

  

  An 
  important 
  question 
  with 
  clay 
  workers 
  is 
  the 
  regulation 
  of 
  

   the 
  temperature, 
  and 
  the 
  production 
  of 
  similar 
  results 
  during 
  a 
  

   number 
  of 
  successive 
  burnings. 
  It, 
  therefore, 
  becomes 
  neces- 
  

   sary 
  to 
  have 
  some 
  means 
  of 
  judging 
  the 
  temperature 
  of 
  the 
  kiln. 
  

   One 
  method 
  consists 
  in 
  using 
  a 
  testpiece 
  of 
  clay, 
  which 
  shows 
  

   certain 
  effects 
  when 
  the 
  burning 
  has 
  reached 
  the 
  proper 
  point. 
  

   Another 
  method, 
  which 
  is 
  a 
  modification 
  of 
  the 
  one 
  just 
  men- 
  

   tioned, 
  is 
  to 
  use 
  what 
  are 
  known 
  as 
  Segers 
  cones. 
  These 
  are 
  

   little 
  pyramid 
  pieces 
  of 
  clays 
  with 
  other 
  substances 
  of 
  a 
  fluxing 
  

   nature 
  added. 
  They 
  are 
  so 
  compounded 
  that 
  there 
  shall 
  be 
  a 
  con- 
  

   stant 
  difference 
  between 
  their 
  fusing 
  points. 
  These 
  cones 
  are 
  

   numbered 
  from 
  .022 
  to 
  33. 
  The 
  theory 
  of 
  these 
  pyramids 
  

   or 
  cones 
  is 
  that 
  the 
  cone 
  bends 
  over 
  as 
  the 
  temperature 
  

   approaches 
  its 
  fusing 
  point, 
  and 
  when 
  this 
  is 
  reached 
  the 
  tip 
  

   touches 
  the 
  base. 
  

  

  In 
  actual 
  use 
  they 
  are 
  placed 
  in 
  the 
  kiln 
  at 
  a 
  point 
  where 
  they 
  

   can 
  be 
  watched 
  through 
  a 
  peephole, 
  but 
  at 
  the 
  same 
  time 
  will 
  

   not 
  receive 
  the 
  direct 
  touch 
  of 
  the 
  flame 
  from 
  the 
  fuel, 
  and 
  it 
  is 
  

   always 
  well 
  to 
  put 
  two 
  or 
  more 
  in 
  the 
  kiln 
  so 
  thas 
  warning 
  can 
  

   be 
  had 
  of 
  the 
  approach 
  of 
  the 
  desired 
  temperature, 
  as 
  well 
  as 
  of 
  

   the 
  rapidity 
  with 
  which 
  the 
  temperature 
  is 
  rising. 
  

  

  In 
  order 
  to 
  determine 
  the 
  temperature 
  of 
  the 
  kiln 
  several 
  

   cones 
  are 
  put 
  in, 
  as 
  for 
  example, 
  Nos. 
  ,07, 
  i 
  and 
  5. 
  Suppose 
  

  

  