﻿CLAYS 
  OF 
  NEW 
  YORK 
  5 
  Go 
  

  

  on 
  the 
  clay 
  as 
  a 
  mixture 
  of 
  fused 
  particles, 
  with 
  a 
  skeleton 
  of 
  un- 
  

   fused 
  ones. 
  If 
  the 
  proportion 
  of 
  the 
  former 
  to 
  the 
  latter 
  is 
  very 
  

   small, 
  there 
  will 
  be 
  a 
  strong 
  hardening 
  of 
  the 
  clay 
  with 
  little 
  

   shrinkage, 
  and 
  the 
  burned 
  clay 
  will 
  still 
  be 
  porous. 
  With 
  an 
  in- 
  

   crease 
  of 
  temperature, 
  and 
  the 
  fusion 
  of 
  more 
  particles, 
  the 
  pores 
  

   fill 
  up 
  more 
  and 
  more, 
  and 
  the 
  shrinkage 
  goes 
  on 
  till 
  at 
  the 
  point 
  

   of 
  vitrification 
  the 
  spaces 
  are 
  completely 
  filled. 
  Above 
  this 
  point 
  

   there 
  is 
  no 
  longer 
  a 
  sufiiciently 
  strong 
  skeleton 
  to 
  hold 
  the 
  mass 
  

   together, 
  and 
  the 
  clay 
  begins 
  to 
  flow. 
  

  

  The 
  conditions 
  which 
  influence 
  the 
  difference 
  in 
  temperature 
  

   between 
  vitrification 
  and 
  viscosity 
  still 
  remain 
  to 
  be 
  satisfactorily 
  

   explained, 
  but 
  it 
  probably 
  depends 
  on 
  the 
  relative 
  amounts 
  of 
  

   fluxes 
  and 
  nonfluxes, 
  and 
  the 
  size 
  of 
  grain 
  of 
  the 
  latter. 
  

  

  The 
  preservation 
  of 
  form 
  in 
  burning 
  is 
  primarily 
  dependent 
  on 
  

   the 
  refractoriness 
  of 
  the 
  mineralogic 
  components 
  which 
  are 
  pres- 
  

   ent 
  in 
  the 
  greatest 
  quantity, 
  because 
  these 
  build 
  a 
  framework 
  or 
  

   skeleton. 
  In 
  kaolins 
  and 
  some 
  refractory 
  clays 
  this 
  component 
  is 
  

   the 
  clay 
  substance. 
  

  

  A 
  feldspar 
  percentage 
  aids 
  the 
  fusion 
  above 
  a 
  certain 
  tempera- 
  

   ture. 
  At 
  high 
  temperatures 
  the 
  quartz 
  tends 
  to 
  increase 
  the 
  fluid- 
  

   ity 
  of 
  the 
  fused 
  clay, 
  but 
  at 
  lower 
  temperatures 
  the 
  quartz 
  is 
  to 
  be 
  

   classed 
  with 
  those 
  components 
  which 
  aid 
  in 
  preserving 
  the 
  form, 
  

   and 
  in 
  low 
  grade 
  clays 
  the 
  quartz 
  has 
  an 
  important 
  office 
  in 
  this 
  

   connection. 
  

  

  The 
  recent 
  experiments 
  of 
  Hofman 
  lead 
  him 
  to 
  believe 
  that 
  size 
  

   of 
  grain 
  does 
  not 
  influence 
  the 
  refractory 
  qualities 
  of 
  a 
  clay 
  {Trans. 
  

   Amer. 
  dnst. 
  min. 
  eng. 
  Oct. 
  1898), 
  and 
  in 
  the 
  case 
  of 
  fire 
  clays 
  

   tested 
  by 
  him 
  this 
  seems 
  to 
  be 
  true. 
  

  

  