﻿CLAYS 
  OF 
  ]N'EW 
  YORK 
  5 
  i3 
  

  

  A 
  fourtli 
  plan 
  is 
  to 
  press 
  the 
  mixed 
  clay 
  into 
  a 
  form 
  of 
  given 
  

   thickness, 
  and 
  tlien 
  bring 
  a 
  metal 
  cylinder 
  to 
  bear 
  on 
  the 
  upper 
  

   surface. 
  This 
  cylinder 
  can 
  be 
  weighed, 
  and 
  the 
  weight 
  be 
  noted 
  

   which 
  has 
  to 
  be 
  added 
  in 
  order 
  to 
  force 
  the 
  cylinder 
  through 
  the 
  

   clay 
  in 
  a 
  given 
  time; 
  or 
  the 
  determination 
  may 
  be 
  made 
  by 
  measur- 
  

   ing 
  the 
  amount 
  of 
  w^ater 
  mixed 
  mth 
  the 
  clay 
  in 
  order 
  to 
  produce 
  

   the 
  proper 
  consistency 
  to 
  permit 
  the 
  passage 
  of 
  the 
  cylinder 
  through 
  

   the 
  clay 
  in 
  a 
  certain 
  time 
  under 
  given 
  pressure. 
  

  

  Olchewsky^ 
  states 
  that 
  the 
  amount 
  required 
  for 
  lean 
  clays 
  is 
  

   as 
  low 
  as 
  17^, 
  while 
  for 
  very 
  plastic 
  clays 
  it 
  is 
  not 
  uncommonly 
  50^. 
  

  

  Bischof 
  has 
  suggested 
  forcing 
  the 
  wet 
  clay 
  from 
  a 
  circular 
  open- 
  

   ing 
  in 
  the 
  lower 
  end 
  of 
  a 
  vertical 
  cylinder, 
  and 
  observing 
  the 
  length 
  

   oi 
  the 
  clay 
  which 
  would 
  issue 
  before 
  the 
  mass 
  broke. 
  This 
  is 
  not, 
  

   however, 
  an 
  accurate 
  method. 
  

  

  The 
  difference 
  in 
  plasticity 
  between 
  residual 
  and 
  sedimentary 
  

   clays 
  is 
  dwelt 
  on 
  by 
  Seger, 
  who 
  says: 
  

  

  In 
  clays 
  which 
  show 
  a 
  mixture 
  of 
  plastic 
  and 
  nonplastic 
  parti- 
  

   cles 
  the 
  degTce 
  of 
  plasticity 
  depends 
  on 
  the 
  relations 
  existing 
  be- 
  

   tween 
  the 
  two. 
  We 
  also 
  know 
  that 
  the 
  true 
  clay 
  substance 
  [meaning 
  

   kaolinite], 
  even 
  when 
  of 
  constant 
  composition, 
  may 
  show 
  con- 
  

   siderable 
  variation 
  in 
  plasticity. 
  One 
  clay 
  substance 
  may 
  be 
  lean 
  

   and 
  permit 
  of 
  very 
  little 
  admixture 
  of 
  nonplastic 
  particles, 
  while 
  

   another 
  may 
  be 
  very 
  fat 
  and 
  permit 
  considerable 
  material 
  being 
  

   mixed 
  in, 
  and 
  still 
  be 
  not 
  only 
  plastic 
  but 
  dry 
  to 
  a 
  hard 
  mass. 
  The 
  

   former 
  case 
  is 
  generally 
  to 
  be 
  found 
  in 
  residual 
  clays, 
  the 
  latter 
  

   in 
  sedimentary. 
  

  

  Seger 
  considered 
  it 
  unsettled 
  whether 
  this 
  is 
  due 
  to 
  a 
  finer 
  

   state 
  of 
  division, 
  or 
  the 
  introduction 
  of 
  plastic 
  particles 
  not 
  derived 
  

   from 
  the 
  feldspar. 
  

  

  The 
  degree 
  of 
  hardness 
  which 
  clays 
  assume 
  on 
  drying 
  also 
  stands 
  

   in 
  direct 
  relation 
  to 
  the 
  plasticity. 
  Slightly 
  plastic 
  kaolins 
  when 
  

   dry 
  give 
  only 
  a 
  loosely 
  knit 
  mass. 
  This 
  point 
  as 
  well 
  was 
  com- 
  

   mented 
  on 
  by 
  Seger 
  in 
  comparing 
  two 
  clays 
  of 
  nearly 
  the 
  same 
  com- 
  

  

  ' 
  Post. 
  Chem. 
  tech. 
  analyse. 
  1890. 
  v. 
  2, 
  pt 
  1, 
  p. 
  43. 
  

  

  