﻿CLAYS 
  OF 
  NEW 
  YORK 
  

  

  637 
  

  

  age 
  of 
  the 
  clay 
  in 
  the 
  burning, 
  and 
  it 
  will 
  be 
  the 
  more 
  injurious 
  the 
  

   less 
  finely 
  divided 
  its 
  condition; 
  consequently 
  if 
  a 
  brick 
  clay 
  con- 
  

   tains 
  lime 
  it 
  should 
  be 
  seen 
  to 
  that 
  the 
  substance 
  is 
  finely 
  and 
  

   evenly 
  disseminated 
  throughout 
  the 
  material, 
  for 
  if 
  in 
  lumps 
  it 
  is 
  

   very 
  apt 
  to 
  split 
  the 
  burned 
  brick. 
  Many 
  brick 
  clays 
  which 
  con- 
  

   tain 
  lime 
  pebbles 
  are 
  often 
  dried 
  and 
  screened 
  before 
  using. 
  

  

  Sand 
  decreases 
  both 
  the 
  plasticity 
  and 
  the 
  tensile 
  strength 
  of 
  the 
  

   clay 
  as 
  well 
  as 
  the 
  shrinkage. 
  This 
  fact 
  is 
  frequently 
  known 
  and 
  

   utilized 
  by 
  the 
  manufacturer 
  to 
  diminish 
  the 
  shrinkage 
  of 
  his 
  clay 
  

   in 
  both 
  drying 
  and 
  burning, 
  consequently 
  reducing 
  the 
  danger 
  of 
  

   obtaining 
  a 
  warped 
  or 
  cracked 
  product. 
  Some 
  clays 
  will 
  stand 
  as 
  

   much 
  as 
  25^ 
  of 
  sand. 
  The 
  coarser 
  the 
  sand, 
  the 
  more 
  marked 
  will 
  

   be 
  its 
  effect 
  on 
  the 
  shrinkage. 
  On 
  the 
  other 
  hand, 
  if 
  the 
  grains 
  

   of 
  sand 
  are 
  angular 
  and 
  of 
  too 
  large 
  size, 
  they 
  may 
  of 
  themselves 
  

   produce 
  a 
  cracking 
  of 
  the 
  ware; 
  and 
  it 
  should 
  be 
  borne 
  in 
  mind 
  that 
  

   there 
  is 
  danger 
  of 
  adding 
  too 
  much 
  sand 
  to 
  a 
  clay, 
  for 
  the 
  tendency 
  

   will 
  be 
  to 
  produce 
  a 
  weak, 
  porous 
  brick, 
  specially 
  if 
  the 
  latter 
  is 
  

   hand-molded. 
  

  

  Fine-gTained 
  clays 
  and 
  very 
  plastic 
  ones 
  generally 
  need 
  to 
  be 
  

   dried 
  very 
  slowly, 
  the 
  reason 
  being 
  that 
  on 
  account 
  of 
  the 
  smallness 
  

   of 
  the 
  pores 
  the 
  moisture 
  can 
  not 
  escape 
  readily, 
  and 
  the 
  outer 
  por- 
  

   tion 
  of 
  the 
  brick 
  dries 
  and 
  shrinks 
  more 
  quickly 
  than 
  the 
  interior, 
  

   with 
  the 
  resultant 
  cracking. 
  Rapid 
  drying 
  may 
  be 
  prevented 
  

   somewhat 
  by 
  adding 
  salt 
  water 
  to 
  the 
  clay, 
  and 
  this 
  is 
  a 
  common 
  

   practice 
  in 
  parts 
  of 
  Missouri. 
  (Mo. 
  geol. 
  sur. 
  11: 
  481) 
  

  

  Fine-grained 
  clays 
  often 
  have 
  to 
  be 
  heated 
  slowly 
  in 
  the 
  early 
  

   stages 
  of 
  burning, 
  though 
  if 
  such 
  a 
  clay 
  contains 
  an 
  abundance 
  of 
  

   fine 
  sand 
  particles, 
  the 
  contrary 
  is 
  possible. 
  

  

  