﻿510 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  PROPERTIES 
  OF 
  CLAY 
  

  

  Pure 
  clay 
  would 
  be 
  composed 
  entirely 
  of 
  the 
  mineral 
  kaolinite, 
  

   the 
  hydrated 
  silicate 
  of 
  alumina. 
  A 
  mass 
  of 
  it 
  would 
  be 
  called 
  

   kaolin. 
  '^Ilie 
  latter 
  is 
  the 
  name 
  of 
  the 
  rock, 
  the 
  former 
  the 
  name 
  

   of 
  the 
  mineral 
  composing 
  it. 
  

  

  Pure 
  kaolin 
  has 
  not 
  been 
  found 
  thus 
  far, 
  Irhough 
  deposits 
  con- 
  

   taining 
  as 
  much 
  as 
  70fo 
  of 
  kaolinite 
  are 
  known, 
  and 
  these 
  when 
  

   washed 
  yield 
  in 
  some 
  instances 
  a 
  mass 
  containing 
  as 
  much 
  as 
  98.5/^ 
  

   of 
  kaolinite. 
  Kaolin 
  therefore 
  contains 
  a 
  yariable 
  amount 
  of 
  

   foreign 
  minerals, 
  mixed 
  with 
  the 
  kaolinite, 
  or 
  clay 
  substance, 
  as 
  it 
  

   is 
  sometimes 
  .called. 
  These 
  impui'ities 
  affect 
  the 
  properties 
  of 
  

   the 
  kaolin 
  materially, 
  either 
  as 
  regards 
  its 
  shrinkage, 
  fusibility, 
  

   or 
  color 
  in 
  burning. 
  The 
  last 
  named 
  effect 
  is 
  caused 
  by 
  the 
  

   presence 
  of 
  ferruginous 
  impurities. 
  Their 
  presence 
  in 
  an 
  effective 
  

   amount 
  would 
  necessitate 
  classing 
  the 
  material 
  with 
  residual 
  clay. 
  

  

  Kaolinite 
  is 
  supposed 
  to 
  form 
  the 
  base 
  of 
  all 
  clays, 
  or 
  kaolinite 
  

   together 
  with 
  other 
  hydrated 
  silicates 
  of 
  alumina. 
  This 
  clay 
  sub- 
  

   stance 
  forms 
  a 
  variable 
  proportion 
  of 
  the 
  clay 
  mass, 
  and 
  stands 
  in 
  

   no 
  direct 
  relation 
  to 
  the 
  plasticity, 
  except 
  that 
  plasticity 
  is 
  lost 
  

   with 
  the 
  expulsion 
  of 
  the 
  coimbined 
  water. 
  The 
  amount 
  of 
  clay 
  

   substance 
  ranges 
  in 
  known 
  clays 
  from 
  5fo 
  or 
  lOfc 
  to 
  98.5^. 
  The 
  

   former 
  might, 
  be 
  a 
  clay 
  sand, 
  the 
  latter 
  a 
  nearly 
  pure 
  kaolin. 
  In 
  

   kaolins 
  the 
  chief 
  impurities 
  are 
  quartz, 
  feldspar 
  and 
  mica, 
  l^ut 
  

   in 
  other 
  clays 
  the 
  number 
  of 
  mineral 
  impurities 
  may 
  be 
  very 
  large. 
  

   (See 
  chapter 
  on 
  " 
  Mineralogy 
  of 
  .clays 
  " 
  p. 
  503) 
  

  

  The 
  properties 
  of 
  clay 
  fall 
  generally 
  under 
  two 
  heads, 
  chemical 
  

   and 
  physical. 
  The 
  latter 
  includes 
  plasticity, 
  fusibility, 
  shrink- 
  

   age, 
  tensile 
  strength, 
  slaking, 
  absorption, 
  density. 
  The 
  former 
  em- 
  

   braces 
  the 
  chemical 
  composition, 
  wdiich 
  exerts 
  an 
  influence 
  on 
  the 
  

   physical 
  behavior 
  of 
  the 
  clay 
  and 
  should 
  therefore 
  be 
  discussed 
  

   first. 
  

  

  