﻿CLAYS 
  OF 
  Is'EW 
  YORK 
  529 
  

  

  of 
  moisture 
  present 
  in 
  a 
  clay 
  depends 
  on 
  the 
  number 
  and 
  size 
  of 
  the 
  

   spaces 
  between 
  the 
  clay 
  grains, 
  the 
  size 
  of 
  the 
  clay 
  particles, 
  and 
  

   the 
  amount 
  of 
  organic 
  matter 
  present. 
  

  

  Air 
  drying 
  usually 
  causes 
  the 
  evaporation 
  of 
  most 
  of 
  the 
  water 
  in 
  

   a 
  clay, 
  accompanied 
  by 
  a 
  shrinkage 
  of 
  the 
  mass, 
  which 
  ceases 
  how- 
  

   ever 
  before 
  all 
  the 
  moisture 
  has 
  passed 
  off. 
  The 
  reason 
  for 
  this 
  is 
  

   that 
  the 
  shrinkage 
  of 
  the 
  clay 
  ceases 
  when 
  the 
  particles 
  come 
  in 
  

   contact, 
  which 
  may 
  happen 
  and 
  still 
  leave 
  interstices. 
  These 
  of 
  

   course 
  still 
  contain 
  moisture, 
  and 
  consequently 
  the 
  brick 
  will 
  keep 
  

   on 
  losing 
  weight 
  till 
  not 
  only 
  this 
  interstitial 
  water, 
  but 
  also 
  the 
  

   surface 
  moisture 
  of 
  the 
  particles, 
  is 
  driven 
  off. 
  In 
  practice, 
  it 
  is 
  

   this 
  that 
  evaporates 
  during 
  the 
  first 
  period 
  of 
  the 
  burning 
  known 
  as 
  

   " 
  water-smoking." 
  The 
  shrinkage 
  of 
  the 
  clay 
  attendant 
  on 
  drying 
  

   varies,, 
  with 
  the 
  nature 
  of 
  the 
  material, 
  from 
  2^ 
  or 
  3^ 
  to 
  10^ 
  or 
  even 
  

   15^. 
  It 
  is 
  governed 
  largely 
  by 
  the 
  causes 
  influencing 
  the 
  absorption 
  

   of 
  the 
  clay. 
  

  

  Sandy 
  clays 
  usually 
  show 
  the 
  least 
  shrinkage, 
  and 
  of 
  this 
  kind 
  

   the 
  coarser 
  grained 
  diminish 
  in 
  size 
  the 
  least. 
  Highly 
  plastic 
  clays 
  

   generally 
  show 
  the 
  highest 
  shrinkage. 
  

  

  The 
  amount 
  of 
  water 
  which 
  a 
  dry 
  clay 
  needs 
  in 
  order 
  to 
  develop 
  

   its 
  maximum 
  plasticity 
  is 
  a 
  variable 
  quantity. 
  Plastic 
  clays 
  absorl) 
  

   lai'ge 
  quantities 
  of 
  water, 
  but 
  a 
  lean 
  clay 
  if 
  fine-grained 
  may 
  do 
  

   the 
  same. 
  As 
  a 
  very 
  general 
  rule 
  it 
  may 
  be 
  stated 
  that 
  lean 
  clays 
  

   absorb 
  from 
  12;fc-20;^, 
  while 
  fat 
  clays 
  requii'O 
  anywhere 
  from 
  

   25^-50^; 
  and 
  the 
  more 
  water 
  a 
  clay 
  absorbs, 
  the 
  more 
  it 
  has 
  to 
  part 
  

   with 
  in 
  drying 
  and 
  the 
  greater 
  will 
  be 
  its 
  shrinkage. 
  

  

  Highly 
  aluminous 
  clays 
  do 
  not 
  always 
  absorb 
  the 
  most 
  water, 
  

   nor 
  are 
  they 
  the 
  most 
  plastic. 
  Some 
  clays 
  low 
  in 
  alumina 
  and 
  high 
  

   in 
  organic 
  matter 
  are 
  not 
  only 
  highly 
  plastic 
  but 
  also 
  absorb 
  a 
  high 
  

   amount 
  of 
  water. 
  

  

  Owing 
  to 
  the 
  high 
  shrinkage 
  of 
  most 
  clays 
  mth 
  high 
  absorptive 
  

   power, 
  there 
  is 
  frequently 
  danger 
  of 
  their 
  cracking, 
  if 
  rapidly 
  dried, 
  

   on 
  account 
  of 
  the 
  active 
  disengagement 
  of 
  water 
  vapor. 
  

  

  