﻿Ill] 
  Special 
  Report 
  No. 
  4 
  : 
  Clays 
  275 
  

  

  At 
  cone 
  5 
  the 
  color 
  was 
  still 
  red 
  and 
  the 
  shrinkage 
  was 
  8 
  per 
  

   cent, 
  while 
  incipient 
  fusion 
  had 
  begun. 
  

  

  At 
  cone 
  26 
  the 
  clay 
  was 
  completely 
  vitrified. 
  

  

  It 
  is 
  to 
  be 
  regarded 
  as 
  a 
  semi-refractor}^ 
  clay, 
  but 
  not 
  good 
  for 
  

   fire-brick. 
  

  

  There 
  was 
  onlj' 
  a 
  trace 
  of 
  soluble 
  salts. 
  

   153. 
  Sec. 
  17, 
  T. 
  3 
  N., 
  R. 
  II 
  W. 
  

  

  This 
  is 
  a 
  soft 
  gritty 
  shale 
  with 
  flakes 
  of 
  mica 
  and 
  much 
  

   organic 
  matter. 
  It 
  took 
  35 
  per 
  cent, 
  of 
  water 
  to 
  work 
  it 
  up 
  but 
  

   did 
  not 
  give 
  a 
  ver}' 
  plastic 
  mass. 
  

  

  The 
  air 
  dried 
  briquettes 
  had 
  a 
  tensile 
  strength 
  of 
  only 
  30 
  lbs. 
  

   per 
  sq. 
  in. 
  

  

  The 
  air 
  shrinkage 
  amounted 
  to 
  9}^ 
  per 
  cent. 
  

  

  At 
  cone 
  i 
  incipient 
  fusion 
  occurred 
  and 
  the 
  color 
  of 
  the 
  

   brick 
  was 
  red. 
  The 
  total 
  shrinkage 
  up 
  to 
  this 
  point 
  was 
  12 
  

   per 
  cent. 
  

  

  At 
  cone 
  5 
  vitrification 
  began 
  and 
  the 
  shrinkage 
  was 
  13 
  

   per 
  cent. 
  

  

  The 
  soluble 
  salts 
  amounted 
  to 
  three-tenths 
  of 
  one 
  per 
  cent, 
  

   which 
  is 
  not 
  excessive, 
  but 
  enough 
  to 
  yield 
  a 
  coating. 
  

  

  While 
  the 
  clay 
  burns 
  dense 
  at 
  a 
  comparatively 
  low 
  tempera- 
  

   ture, 
  viz., 
  cone 
  5, 
  at 
  the 
  same 
  time 
  it 
  lacks 
  in 
  plasticity, 
  and 
  

   if 
  it 
  is 
  desired 
  to 
  use 
  it 
  for 
  paving 
  brick 
  or 
  stoneware 
  it 
  should 
  

   be 
  mixed 
  with 
  a 
  more 
  plastic 
  clay. 
  

  

  In 
  conclusion 
  it 
  may 
  be 
  said 
  that 
  all 
  of 
  the 
  clays 
  submitted 
  

   would, 
  when 
  used 
  alone 
  work 
  for 
  pressed 
  brick, 
  one 
  for 
  paving 
  

   brick 
  and 
  two 
  for 
  earthenware. 
  

  

  Attention 
  should 
  be 
  called 
  to 
  the 
  fact 
  that 
  the 
  points 
  of 
  incip- 
  

   ient 
  fusion 
  of 
  all 
  lie 
  somewhat 
  higher 
  than 
  they 
  do 
  in 
  most 
  brick 
  

   clays, 
  and 
  therefore 
  the 
  best 
  results 
  will 
  be 
  obtained 
  by 
  burning 
  

   them 
  in 
  permanent 
  walled 
  kilns. 
  

  

  There 
  is 
  a 
  great 
  tendency 
  among 
  Southern 
  brickmakers 
  to 
  not 
  

   only 
  underburn 
  their 
  bricks, 
  but 
  also 
  to 
  mix 
  sand 
  with 
  the 
  clay, 
  

   when 
  there 
  is 
  already 
  enough 
  sand 
  in 
  it. 
  

  

  