﻿530 
  NEW 
  YORK 
  STATE 
  MUSEUM 
  

  

  Moisture 
  may 
  play 
  another 
  important 
  and 
  injurious 
  role 
  in 
  the 
  

   working 
  of 
  a 
  clay, 
  in 
  that 
  it 
  tends 
  to 
  dissolve 
  soluble 
  salts 
  in 
  the 
  

   clay, 
  and 
  bring 
  them 
  tO' 
  the 
  surface 
  in 
  drying, 
  giving 
  rise 
  to 
  the 
  

   formation 
  of 
  efflorescence. 
  It 
  may 
  also 
  permit 
  acids 
  contained 
  in 
  

   the 
  fir© 
  gases 
  of 
  the 
  kiln 
  to 
  act 
  on 
  the 
  mineral 
  ingredients 
  of 
  the 
  

   clay 
  and 
  thus 
  form 
  soluble 
  compounds, 
  specially 
  sulfates 
  and 
  

   chlorids. 
  

  

  By 
  the 
  addition 
  of 
  water 
  to 
  an 
  air-dried 
  clay, 
  it 
  gradually 
  passes 
  

   from 
  a 
  powdery 
  or 
  lumpy 
  condition 
  to 
  a 
  pasty 
  mass, 
  the 
  tenacious- 
  

   ness 
  of 
  which 
  increases 
  tillthe 
  point 
  of 
  maximum 
  plasticity 
  for 
  the 
  

   given 
  clay 
  is 
  reached. 
  If 
  the 
  addition 
  of 
  water 
  be 
  continued, 
  the 
  

   clay 
  gradually 
  passes 
  into 
  a 
  soft 
  mud. 
  In 
  some 
  clays 
  this 
  change 
  

   takes 
  place 
  slowly, 
  in 
  others 
  (specially 
  many 
  residual 
  clays) 
  very 
  

   rapidly. 
  

  

  Combined 
  water 
  is 
  present 
  in 
  every 
  clay. 
  In 
  pure 
  kaolin 
  there 
  is 
  

   nearly 
  14^, 
  and 
  amounts 
  are 
  found 
  in 
  different 
  clays 
  intermediate 
  

   between 
  this 
  and 
  Sfo 
  or 
  4^. 
  

  

  The 
  sources 
  of 
  combined 
  water 
  in 
  clays 
  are 
  either 
  kaolinite, 
  

   limonite, 
  or 
  hydrated 
  silicates; 
  the 
  quantity 
  in 
  different 
  clays 
  can 
  

   be 
  seen 
  from 
  the 
  table 
  of 
  analyses 
  given 
  at 
  the 
  end 
  of 
  the 
  report. 
  

  

  It 
  is 
  driven 
  off 
  at 
  a 
  low 
  red 
  heat; 
  and 
  when 
  this 
  occurs 
  an 
  addi- 
  

   tional 
  shrinkage 
  takes 
  place, 
  the 
  extent 
  depending 
  on 
  the 
  quantity 
  

   of 
  water 
  present. 
  The 
  shrinkage 
  varies 
  commonly 
  from 
  2^-10^ 
  or 
  

   even 
  14^. 
  

  

  While 
  the 
  amount 
  of 
  combined 
  water 
  does 
  not 
  seem 
  to 
  stand 
  in 
  

   direct 
  relation 
  to 
  the 
  plasticity 
  of 
  the 
  clay, 
  nevertheless, 
  when 
  it 
  is 
  

   once 
  driven 
  off, 
  the 
  clay 
  can 
  no 
  longer 
  be 
  rendered 
  plastic. 
  

  

  Methods 
  of 
  analyzing 
  clay 
  

  

  By 
  H. 
  T. 
  Vulte 
  Ph.D. 
  

  

  One 
  grain 
  of 
  the 
  dried 
  and 
  finely 
  pulverized 
  clay 
  is 
  fused 
  in 
  a 
  

   platinum 
  crucible 
  with 
  five 
  to 
  10 
  times 
  its 
  weight 
  of 
  a 
  mixture 
  of 
  

   11 
  parts 
  of 
  dry 
  sodium 
  carbonate 
  and 
  14 
  parts 
  of 
  dry 
  potassium 
  

   carbonate, 
  the 
  amount 
  of 
  fusion 
  mixture 
  necessary 
  depending 
  on 
  the 
  

  

  